Is it possible to create a template string as a usual string,
let a = "b:${b}";
and then convert it into a template string,
let b = 10;
console.log(a.template()); // b:10
without eval, new Function and other means of dynamic code generation?
In my project I've created something like this with ES6:
String.prototype.interpolate = function(params) {
const names = Object.keys(params);
const vals = Object.values(params);
return new Function(...names, `return \`${this}\`;`)(...vals);
}
const template = 'Example text: ${text}';
const result = template.interpolate({
text: 'Foo Boo'
});
console.log(result);
As your template string must get reference to the b variable dynamically (in runtime), so the answer is: NO, it's impossible to do it without dynamic code generation.
But, with eval it's pretty simple:
let tpl = eval('`'+a+'`');
No, there is not a way to do this without dynamic code generation.
However, I have created a function which will turn a regular string into a function which can be provided with a map of values, using template strings internally.
Generate Template String Gist
/**
* Produces a function which uses template strings to do simple interpolation from objects.
*
* Usage:
* var makeMeKing = generateTemplateString('${name} is now the king of ${country}!');
*
* console.log(makeMeKing({ name: 'Bryan', country: 'Scotland'}));
* // Logs 'Bryan is now the king of Scotland!'
*/
var generateTemplateString = (function(){
var cache = {};
function generateTemplate(template){
var fn = cache[template];
if (!fn){
// Replace ${expressions} (etc) with ${map.expressions}.
var sanitized = template
.replace(/\$\{([\s]*[^;\s\{]+[\s]*)\}/g, function(_, match){
return `\$\{map.${match.trim()}\}`;
})
// Afterwards, replace anything that's not ${map.expressions}' (etc) with a blank string.
.replace(/(\$\{(?!map\.)[^}]+\})/g, '');
fn = Function('map', `return \`${sanitized}\``);
}
return fn;
}
return generateTemplate;
})();
Usage:
var kingMaker = generateTemplateString('${name} is king!');
console.log(kingMaker({name: 'Bryan'}));
// Logs 'Bryan is king!' to the console.
Hope this helps somebody. If you find a problem with the code, please be so kind as to update the Gist.
What you're asking for here:
//non working code quoted from the question
let b=10;
console.log(a.template());//b:10
is exactly equivalent (in terms of power and, er, safety) to eval: the ability to take a string containing code and execute that code; and also the ability for the executed code to see local variables in the caller's environment.
There is no way in JS for a function to see local variables in its caller, unless that function is eval(). Even Function() can't do it.
When you hear there's something called "template strings" coming to JavaScript, it's natural to assume it's a built-in template library, like Mustache. It isn't. It's mainly just string interpolation and multiline strings for JS. I think this is going to be a common misconception for a while, though. :(
There are many good solutions posted here, but none yet which utilizes the ES6 String.raw method. Here is my contriubution. It has an important limitation in that it will only accept properties from a passed in object, meaning no code execution in the template will work.
function parseStringTemplate(str, obj) {
let parts = str.split(/\$\{(?!\d)[\wæøåÆØÅ]*\}/);
let args = str.match(/[^{\}]+(?=})/g) || [];
let parameters = args.map(argument => obj[argument] || (obj[argument] === undefined ? "" : obj[argument]));
return String.raw({ raw: parts }, ...parameters);
}
let template = "Hello, ${name}! Are you ${age} years old?";
let values = { name: "John Doe", age: 18 };
parseStringTemplate(template, values);
// output: Hello, John Doe! Are you 18 years old?
Split string into non-argument textual parts. See regex.
parts: ["Hello, ", "! Are you ", " years old?"]
Split string into property names. Empty array if match fails.
args: ["name", "age"]
Map parameters from obj by property name. Solution is limited by shallow one level mapping. Undefined values are substituted with an empty string, but other falsy values are accepted.
parameters: ["John Doe", 18]
Utilize String.raw(...) and return result.
TLDR:
https://jsfiddle.net/bj89zntu/1/
Everyone seems to be worried about accessing variables. Why not just pass them? I'm sure it won't be too hard to get the variable context in the caller and pass it down. Use
ninjagecko's answer to get the props from obj.
function renderString(str,obj){
return str.replace(/\$\{(.+?)\}/g,(match,p1)=>{return index(obj,p1)})
}
Here is the full code:
function index(obj,is,value) {
if (typeof is == 'string')
is=is.split('.');
if (is.length==1 && value!==undefined)
return obj[is[0]] = value;
else if (is.length==0)
return obj;
else
return index(obj[is[0]],is.slice(1), value);
}
function renderString(str,obj){
return str.replace(/\$\{.+?\}/g,(match)=>{return index(obj,match)})
}
renderString('abc${a}asdas',{a:23,b:44}) //abc23asdas
renderString('abc${a.c}asdas',{a:{c:22,d:55},b:44}) //abc22asdas
The issue here is to have a function that has access to the variables of its caller. This is why we see direct eval being used for template processing. A possible solution would be to generate a function taking formal parameters named by a dictionary's properties, and calling it with the corresponding values in the same order. An alternative way would be to have something simple as this:
var name = "John Smith";
var message = "Hello, my name is ${name}";
console.log(new Function('return `' + message + '`;')());
And for anyone using Babel compiler we need to create closure which remembers the environment in which it was created:
console.log(new Function('name', 'return `' + message + '`;')(name));
I liked s.meijer's answer and wrote my own version based on his:
function parseTemplate(template, map, fallback) {
return template.replace(/\$\{[^}]+\}/g, (match) =>
match
.slice(2, -1)
.trim()
.split(".")
.reduce(
(searchObject, key) => searchObject[key] || fallback || match,
map
)
);
}
Similar to Daniel's answer (and s.meijer's gist) but more readable:
const regex = /\${[^{]+}/g;
export default function interpolate(template, variables, fallback) {
return template.replace(regex, (match) => {
const path = match.slice(2, -1).trim();
return getObjPath(path, variables, fallback);
});
}
//get the specified property or nested property of an object
function getObjPath(path, obj, fallback = '') {
return path.split('.').reduce((res, key) => res[key] || fallback, obj);
}
Note: This slightly improves s.meijer's original, since it won't match things like ${foo{bar} (the regex only allows non-curly brace characters inside ${ and }).
UPDATE: I was asked for an example using this, so here you go:
const replacements = {
name: 'Bob',
age: 37
}
interpolate('My name is ${name}, and I am ${age}.', replacements)
#Mateusz Moska, solution works great, but when i used it in React Native(build mode), it throws an error: Invalid character '`', though it works when i run it in debug mode.
So i wrote down my own solution using regex.
String.prototype.interpolate = function(params) {
let template = this
for (let key in params) {
template = template.replace(new RegExp('\\$\\{' + key + '\\}', 'g'), params[key])
}
return template
}
const template = 'Example text: ${text}',
result = template.interpolate({
text: 'Foo Boo'
})
console.log(result)
Demo: https://es6console.com/j31pqx1p/
NOTE: Since I don't know the root cause of an issue, i raised a ticket in react-native repo, https://github.com/facebook/react-native/issues/14107, so that once they can able to fix/guide me about the same :)
You can use the string prototype, for example
String.prototype.toTemplate=function(){
return eval('`'+this+'`');
}
//...
var a="b:${b}";
var b=10;
console.log(a.toTemplate());//b:10
But the answer of the original question is no way.
I required this method with support for Internet Explorer. It turned out the back ticks aren't supported by even IE11. Also; using eval or it's equivalent Function doesn't feel right.
For the one that notice; I also use backticks, but these ones are removed by compilers like babel. The methods suggested by other ones, depend on them on run-time. As said before; this is an issue in IE11 and lower.
So this is what I came up with:
function get(path, obj, fb = `$\{${path}}`) {
return path.split('.').reduce((res, key) => res[key] || fb, obj);
}
function parseTpl(template, map, fallback) {
return template.replace(/\$\{.+?}/g, (match) => {
const path = match.substr(2, match.length - 3).trim();
return get(path, map, fallback);
});
}
Example output:
const data = { person: { name: 'John', age: 18 } };
parseTpl('Hi ${person.name} (${person.age})', data);
// output: Hi John (18)
parseTpl('Hello ${person.name} from ${person.city}', data);
// output: Hello John from ${person.city}
parseTpl('Hello ${person.name} from ${person.city}', data, '-');
// output: Hello John from -
I currently can't comment on existing answers so I am unable to directly comment on Bryan Raynor's excellent response. Thus, this response is going to update his answer with a slight correction.
In short, his function fails to actually cache the created function, so it will always recreate, regardless of whether it's seen the template before. Here is the corrected code:
/**
* Produces a function which uses template strings to do simple interpolation from objects.
*
* Usage:
* var makeMeKing = generateTemplateString('${name} is now the king of ${country}!');
*
* console.log(makeMeKing({ name: 'Bryan', country: 'Scotland'}));
* // Logs 'Bryan is now the king of Scotland!'
*/
var generateTemplateString = (function(){
var cache = {};
function generateTemplate(template){
var fn = cache[template];
if (!fn){
// Replace ${expressions} (etc) with ${map.expressions}.
var sanitized = template
.replace(/\$\{([\s]*[^;\s\{]+[\s]*)\}/g, function(_, match){
return `\$\{map.${match.trim()}\}`;
})
// Afterwards, replace anything that's not ${map.expressions}' (etc) with a blank string.
.replace(/(\$\{(?!map\.)[^}]+\})/g, '');
fn = cache[template] = Function('map', `return \`${sanitized}\``);
}
return fn;
};
return generateTemplate;
})();
Still dynamic but seems more controlled than just using a naked eval:
const vm = require('vm')
const moment = require('moment')
let template = '### ${context.hours_worked[0].value} \n Hours worked \n #### ${Math.abs(context.hours_worked_avg_diff[0].value)}% ${fns.gt0(context.hours_worked_avg_diff[0].value, "more", "less")} than usual on ${fns.getDOW(new Date())}'
let context = {
hours_worked:[{value:10}],
hours_worked_avg_diff:[{value:10}],
}
function getDOW(now) {
return moment(now).locale('es').format('dddd')
}
function gt0(_in, tVal, fVal) {
return _in >0 ? tVal: fVal
}
function templateIt(context, template) {
const script = new vm.Script('`'+template+'`')
return script.runInNewContext({context, fns:{getDOW, gt0 }})
}
console.log(templateIt(context, template))
https://repl.it/IdVt/3
I made my own solution doing a type with a description as a function
export class Foo {
...
description?: Object;
...
}
let myFoo:Foo = {
...
description: (a,b) => `Welcome ${a}, glad to see you like the ${b} section`.
...
}
and so doing:
let myDescription = myFoo.description('Bar', 'bar');
I came up with this implementation and it works like a charm.
function interpolateTemplate(template: string, args: any): string {
return Object.entries(args).reduce(
(result, [arg, val]) => result.replace(`$\{${arg}}`, `${val}`),
template,
)
}
const template = 'This is an example: ${name}, ${age} ${email}'
console.log(interpolateTemplate(template,{name:'Med', age:'20', email:'example#abc.com'}))
You could raise an error if arg is not found in template
This solution works without ES6:
function render(template, opts) {
return new Function(
'return new Function (' + Object.keys(opts).reduce((args, arg) => args += '\'' + arg + '\',', '') + '\'return `' + template.replace(/(^|[^\\])'/g, '$1\\\'') + '`;\'' +
').apply(null, ' + JSON.stringify(Object.keys(opts).reduce((vals, key) => vals.push(opts[key]) && vals, [])) + ');'
)();
}
render("hello ${ name }", {name:'mo'}); // "hello mo"
Note: the Function constructor is always created in the global scope, which could potentially cause global variables to be overwritten by the template, e.g. render("hello ${ someGlobalVar = 'some new value' }", {name:'mo'});
You should try this tiny JS module, by Andrea Giammarchi, from github :
https://github.com/WebReflection/backtick-template
/*! (C) 2017 Andrea Giammarchi - MIT Style License */
function template(fn, $str, $object) {'use strict';
var
stringify = JSON.stringify,
hasTransformer = typeof fn === 'function',
str = hasTransformer ? $str : fn,
object = hasTransformer ? $object : $str,
i = 0, length = str.length,
strings = i < length ? [] : ['""'],
values = hasTransformer ? [] : strings,
open, close, counter
;
while (i < length) {
open = str.indexOf('${', i);
if (-1 < open) {
strings.push(stringify(str.slice(i, open)));
open += 2;
close = open;
counter = 1;
while (close < length) {
switch (str.charAt(close++)) {
case '}': counter -= 1; break;
case '{': counter += 1; break;
}
if (counter < 1) {
values.push('(' + str.slice(open, close - 1) + ')');
break;
}
}
i = close;
} else {
strings.push(stringify(str.slice(i)));
i = length;
}
}
if (hasTransformer) {
str = 'function' + (Math.random() * 1e5 | 0);
if (strings.length === values.length) strings.push('""');
strings = [
str,
'with(this)return ' + str + '([' + strings + ']' + (
values.length ? (',' + values.join(',')) : ''
) + ')'
];
} else {
strings = ['with(this)return ' + strings.join('+')];
}
return Function.apply(null, strings).apply(
object,
hasTransformer ? [fn] : []
);
}
template.asMethod = function (fn, object) {'use strict';
return typeof fn === 'function' ?
template(fn, this, object) :
template(this, fn);
};
Demo (all the following tests return true):
const info = 'template';
// just string
`some ${info}` === template('some ${info}', {info});
// passing through a transformer
transform `some ${info}` === template(transform, 'some ${info}', {info});
// using it as String method
String.prototype.template = template.asMethod;
`some ${info}` === 'some ${info}'.template({info});
transform `some ${info}` === 'some ${info}'.template(transform, {info});
Faz assim (This way):
let a = 'b:${this.b}'
let b = 10
function template(templateString, templateVars) {
return new Function('return `' + templateString + '`').call(templateVars)
}
result.textContent = template(a, {b})
<b id=result></b>
Since we're reinventing the wheel on something that would be a lovely feature in javascript.
I use eval(), which is not secure, but javascript is not secure. I readily admit that I'm not excellent with javascript, but I had a need, and I needed an answer so I made one.
I chose to stylize my variables with an # rather than an $, particularly because I want to use the multiline feature of literals without evaluating til it's ready. So variable syntax is #{OptionalObject.OptionalObjectN.VARIABLE_NAME}
I am no javascript expert, so I'd gladly take advice on improvement but...
var prsLiteral, prsRegex = /\#\{(.*?)(?!\#\{)\}/g
for(i = 0; i < myResultSet.length; i++) {
prsLiteral = rt.replace(prsRegex,function (match,varname) {
return eval(varname + "[" + i + "]");
// you could instead use return eval(varname) if you're not looping.
})
console.log(prsLiteral);
}
A very simple implementation follows
myResultSet = {totalrecords: 2,
Name: ["Bob", "Stephanie"],
Age: [37,22]};
rt = `My name is #{myResultSet.Name}, and I am #{myResultSet.Age}.`
var prsLiteral, prsRegex = /\#\{(.*?)(?!\#\{)\}/g
for(i = 0; i < myResultSet.totalrecords; i++) {
prsLiteral = rt.replace(prsRegex,function (match,varname) {
return eval(varname + "[" + i + "]");
// you could instead use return eval(varname) if you're not looping.
})
console.log(prsLiteral);
}
In my actual implementation, I choose to use #{{variable}}. One more set of braces. Absurdly unlikely to encounter that unexpectedly. The regex for that would look like /\#\{\{(.*?)(?!\#\{\{)\}\}/g
To make that easier to read
\#\{\{ # opening sequence, #{{ literally.
(.*?) # capturing the variable name
# ^ captures only until it reaches the closing sequence
(?! # negative lookahead, making sure the following
# ^ pattern is not found ahead of the current character
\#\{\{ # same as opening sequence, if you change that, change this
)
\}\} # closing sequence.
If you're not experienced with regex, a pretty safe rule is to escape every non-alphanumeric character, and don't ever needlessly escape letters as many escaped letters have special meaning to virtually all flavors of regex.
You can refer to this solution
const interpolate = (str) =>
new Function(`return \`${new String(str)}\`;`)();
const foo = 'My';
const obj = {
text: 'Hanibal Lector',
firstNum: 1,
secondNum: 2
}
const str = "${foo} name is : ${obj.text}. sum = ${obj.firstNum} + ${obj.secondNum} = ${obj.firstNum + obj.secondNum}";
console.log(interpolate(str));
I realize I am late to the game, but you could:
const a = (b) => `b:${b}`;
let b = 10;
console.log(a(b)); // b:10
I'm building a PHP Framework for conclusion of my course, and I've stuck on a solution for match some custom routes and standard routes.
My framework's route are similar at routes of Zend Framework 1.
It's match standard routes for
/module/controller/action/param/value/param2/value2/paramn/valuen
The part of URI are optional, and the / route leads to application module, index controller and index action without params and values.
I'm stuck in some custom routes, that I define this way:
/blog/:postname/
/admin/logout/
/blog/posts/:year/:category/
/about/
That routes must match this examples URI requests.
/blog/my-first-post/
/blog/my-first-post/referenced/facebook/
/admin/logout/
/admin/logout/session-id/246753/action
/blog/posts/2013/turism/
/blog/posts/2013/turism/page/2/
But not had to match the standard routes. The custom routes must precede the standard routes.
Some examples of standard routes. Examples:
/
/application/
/application/index/
/application/index/index/
/blog/posts/view/id/3/
/admin/login/
/admin/login/logout (that one are the
/admin/blog/posts/edit/id/3/
/admin/blog/posts/edit/id/3/success/false/
The way I find to do this ellegantily is using RegEx for the matches, but I've trying to learn RegEx for more than one month and don't got it all.
PS: After match the current route, I must to bind the :variable with the related position in the REQUEST_URI.
Thank you for help.
While admittedly tempting, I wouldn't go with regex in this particular case. Even though I usually go that way. A simple loop and match would do, unless your course is setting some restrictions you have to follow.
I put together an example that should get the job done and runs in the console, just to show what i mean.
function get_route($uri){
$routes = [
'blog#show' => 'blog/:postname',
'admin#logout' => 'admin/logout',
'blog#category' => 'blog/posts/:year/:category',
'home#about' => 'about'
];
$params = [];
$uri = preg_replace('/#|\?.+/', '', $uri); // remove hash or query strings
$uri = preg_replace('/(^\/)?(\/$)?/', '', $uri); // trim slashes
$uri = explode('/', $uri);
$action = null;
foreach ($routes as $this_action => $this_route) { // loop through possible routes
$fractions = explode('/', $this_route);
if (sizeof($fractions) !== sizeof($uri)) continue; // did not match length of uri
for ($i=0; $i<sizeof($uri); $i++) { // compare each part of uri to each part of route
if (substr($fractions[$i], 0, 1) !== ':' && $fractions[$i] !== $uri[$i]) break; // not a match and not a param
if ($i === sizeof($uri)-1) { // made it to the last fraction!
$ii = 0;
foreach ($fractions as $fraction) {
if (substr($fraction, 0, 1) == ':') { // it's a param, map it!
$params[substr($fraction,1)] = $uri[$ii];
}
$ii++;
}
return ['action'=>$this_action, 'params'=>$params];
}
}
}
return false;
}
I could reach my needs with this code, a lot of tests has passed.
public function matchCustomRoute($uri)
{
if($uri == '')
{
return null;
}
$customRoutes = $this->getRoutes();
$explodeUri = explode('/', $uri);
$arrayUri = array();
foreach($explodeUri as $uriPart)
{
if($uriPart == '')
{
continue;
}
$arrayUri[] = $uriPart;
}
$countUri = count($arrayUri);
foreach($customRoutes as $key => $value)
{
$explodeRoute = explode('/',$value['route']);
$arrayRoute = array();
foreach($explodeRoute as $routePart)
{
if($routePart == '')
{
continue;
}
$arrayRoute[] = $routePart;
}
$countRoute = count($arrayRoute);
if($countRoute > $countUri)
{
continue;
}
$matches = 0;
for($i = 0 ; $i < $countRoute ; $i++)
{
$match = preg_match('/'.$arrayUri[$i].'/', '/'.$arrayRoute[$i].'/');
if($match == 0)
{
if(substr($arrayRoute[$i], 0, 1) == ':')
{
$value['params'][substr($arrayRoute[$i], 1)] = $arrayUri[$i];
}
else
{
continue;
}
}
$matches++;
}
if($matches == $countRoute)
{
return $value;
}
}
return null;
}
Thank you for help.