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

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I know in PHP we can do something like this:

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

Output: "I pity the foo"

I was wondering if this same thing is possible in JavaScript as well. Using variables inside strings without using concatenation — it looks more concise and elegant to write.

Starting from Firefox 34 / Chrome 41 / Safari 9 / Microsoft Edge you can use an ES2015 / ES6 feature called 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.

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 (Internet Explorer and Safari <= 8), you may want to use Babel 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.

JavaScript Basics: String Concatenation with Variables and , Another way to include a variable to a string is through String Interpolation. In JavaScript, you can insert or interpolate variables into strings using  Using variables inside strings without using concatenation — it looks more concise and elegant to write. javascript string variables string-interpolation share | improve this question

Prior to Firefox 34 / Chrome 41 / Safari 9 / Microsoft Edge, nope, that was not possible in javascript. You would have to resort to:

var hello = "foo";
var my_string = "I pity the " + hello;

How To Work with Strings in JavaScript, Strings in JavaScript are primitive data types and immutable, which means they of strings, how to concatenate strings, how to store strings in variables, and the As there is no convention or official preference for single- or  String interpolation is a really useful programming language feature that allows you to inject variables directly into a string. Until the release of ES6, string interpolation was not available in JavaScript.

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);

How to do String Interpolation with JavaScript, Until the release of ES6, string interpolation was not available in JavaScript. The lack of this feature has lead to horrifying concatenated code that looks like this: No developer wants to maintain a bunch of data that is frankenstein'd together By surrounding the arguments or variables in #{} syntax, ruby makes it possible  javascript string string-interpolation variables. javascript string string-interpolation variables. licensed under cc by-sa 3.0 with attribution.

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

Template literals (Template strings), You can use multi-line strings and string interpolation features with them. In ES2015 with template literals and without nesting: strings—just like the default template function and string concatenation would create. is not defined · ReferenceError: assignment to undeclared variable "x" · ReferenceError:  In this article, we went over the basics of working with strings in JavaScript, from creating and displaying string literals using single and double quotes, creating template literals, concatenation, escaping, and assigning string values to variables.

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'});

String Interpolation in JavaScript, In JavaScript, the template literals (strings wrapped in backticks 4.1 Refactor string concatentation; 4.2 Helper variables; 4.3 Single the sequence of characters "${someCharacters}" without escaping. The string interpolation should be used instead of string concatenation to construct lengthy strings. Definition and Usage. The concat() method is used to join two or more strings. This method does not change the existing strings, but returns a new string containing the text of the joined strings.

Getting Literal With ES6 Template Strings | Web, String interpolation; Embedded expressions; Multiline strings without hacks take any valid JavaScript expression (including say, the addition of variables) and inside a One can also use string concatenation to fake multiline support, but this  Substitution allows us to take any valid JavaScript expression (including say, the addition of variables) and inside a Template Literal, the result will be output as part of the same string. Template Strings can contain placeholders for string substitution using the ${ } syntax, as demonstrated below:

Template Strings in JavaScript, It lets us insert/interpolate variables and expressions into strings without needing to concatenate like in older versions of JavaScript. It allows us  Are there any strong arguments against string interpolation in general? – ksadowski Mar 21 '18 at 15:25 2 @shayne The SQL argument is completely irrelevant to the question, string concatenation is exactly as bad as interpolation, and for exactly the same reasons, in an SQL context. – philomory Oct 18 '18 at 0:37

Yaml concat string with variable, SQL allows us to concatenate strings but the syntax varies according to which database system you are using. In YAML files, any string containing an interpolation token must be quoted. Jan 22, 2015 · JavaScript Errors and How to Fix Them Building Resilient Deploying to Azure Without Writing JSON Arm Templates. The default function just concatenates the parts into a single string. If there is an expression preceding the template literal ( tag here), this is called a "tagged template". In that case, the tag expression (usually a function) gets called with the template literal, which you can then manipulate before outputting.

Comments
  • Don't miss the fact that the template string is delimited with back ticks (`) instead of your normal quote characters. "${foo}" is literally ${foo} `${foo}` is what you actually want
  • Also there are many transpilers to turn ES6 into ES5 to fixed the compatibility issue!
  • when i change a or b value. console.log(Fifteen is ${a + b}.); does not changed dynamically. it always shows Fifteen is 15.
  • It will soon be possible in javascript (ES6) with Template Strings, see my detailed answer below.
  • It is possible if you like to write CoffeeScript, which actually IS javascript with a better syntax.
  • Great shout for older browsers :)
  • Thanks. If you're using dojo, sprintf is available as a module: bill.dojotoolkit.org/api/1.9/dojox/string/sprintf
  • Pretty decent, actually.
  • This answer is good when you need to store template string in database and process it on demand
  • Good one, it works well. very simple but didn't come on mind.
  • Is this efficient?
  • The efficiency will depend largely on the user's browser, since this solution delegates the "heavy lifting" of matching the regex and doing string replacements to the browser's native functions. In any case, since this is happening on the browser-side anyway, efficiency is not such a huge concern. If you want server-side templating (for Node.JS or the like) you should use the ES6 template literals solution described by @bformet, as it is likely more efficient.
  • That doesn't answer the question. You might log out both strings in one line, but that doesn't give you a new string containing both strings, which is what OP is asking for.