How to interpolate variables in strings in JavaScript, without concatenation?

Question

I know in PHP we can do something like this:

$hello = \"foo\";
$my_string = \"I pity the $hello\";

Output: \"I pity the foo\"<

Answer 1

Prior to Firefox 34 / Chrome 41 / Safari 9 / Microsoft Edge, no. Although you could try sprintf for JavaScript to get halfway there:

var hello = "foo";
var my_string = sprintf("I pity the %s", hello);

Answer 2

I wrote this npm package stringinject https://www.npmjs.com/package/stringinject which allows you to do the following

var string = stringInject("this is a {0} string for {1}", ["test", "stringInject"]);

which will replace the {0} and {1} with the array items and return the following string

"this is a test string for stringInject"

or you could replace placeholders with object keys and values like so:

var str = stringInject("My username is {username} on {platform}", { username: "tjcafferkey", platform: "GitHub" });

"My username is tjcafferkey on Github" 

Answer 3

You can take advantage of Template Literals and use this syntax:

`String text ${expression}`

Template literals are enclosed by the back-tick (` `) (grave accent) instead of double or single quotes.

This feature has been introduced in ES2015 (ES6).

Example

var a = 5;
var b = 10;
console.log(`Fifteen is ${a + b}.`);
// "Fifteen is 15.

How neat is that?

Bonus:

It also allows for multi-line strings in javascript without escaping, which is great for templates:

return `
    <div class="${foo}">
         ...
    </div>
`;

Browser support:

As this syntax is not supported by older browsers (mostly Internet Explorer), you may want to use Babel/Webpack to transpile your code into ES5 to ensure it will run everywhere.

---

Side note:

Starting from IE8+ you can use basic string formatting inside console.log:

console.log('%s is %d.', 'Fifteen', 15);
// Fifteen is 15.

Answer 4

Create a method similar to String.format() of Java

StringJoin=(s, r=[])=>{
  r.map((v,i)=>{
    s = s.replace('%'+(i+1),v)
  })
return s
}

use

console.log(StringJoin('I can %1 a %2',['create','method'])) //output: 'I can create a method'

Answer 5

well you could do this, but it's not esp general

'I pity the $fool'.replace('$fool', 'fool')

You could easily write a function that does this intelligently if you really needed to

Answer 6

Complete answer, ready to be used:

 var Strings = {
        create : (function() {
                var regexp = /{([^{]+)}/g;

                return function(str, o) {
                     return str.replace(regexp, function(ignore, key){
                           return (key = o[key]) == null ? '' : key;
                     });
                }
        })()
};

Call as

Strings.create("My firstname is {first}, my last name is {last}", {first:'Neo', last:'Andersson'});

To attach it to String.prototype:

String.prototype.create = function(o) {
           return Strings.create(this, o);
}

Then use as :

"My firstname is ${first}".create({first:'Neo'});