How to interpolate variables in strings in JavaScript, without concatenation?
JavascriptStringVariablesString InterpolationJavascript Problem Overview
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.
Javascript Solutions
Solution 1 - Javascript
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>
`;
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.
Solution 2 - Javascript
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;
Solution 3 - 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);
Solution 4 - Javascript
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
Solution 5 - Javascript
Complete and ready to be used answer for
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'});
If you are on >ES6 then you can also do:
let first = 'Neo';
`My firstname is ${first}`;
Solution 6 - Javascript
You can use this javascript function to do this sort of templating. No need to include an entire library.
function createStringFromTemplate(template, variables) {
return template.replace(new RegExp("\{([^\{]+)\}", "g"), function(_unused, varName){
return variables[varName];
});
}
createStringFromTemplate(
"I would like to receive email updates from {list_name} {var1} {var2} {var3}.",
{
list_name : "this store",
var1 : "FOO",
var2 : "BAR",
var3 : "BAZ"
}
);
Output: "I would like to receive email updates from this store FOO BAR BAZ."
Using a function as an argument to the String.replace() function was part of the ECMAScript v3 spec. See this SO answer for more details.
Solution 7 - Javascript
If you like to write CoffeeScript you could do:
hello = "foo"
my_string = "I pity the #{hello}"
CoffeeScript actually IS javascript, but with a much better syntax.
For an overview of CoffeeScript check this beginner's guide.
Solution 8 - Javascript
I would use the back-tick ``.
let name1 = 'Geoffrey';
let msg1 = `Hello ${name1}`;
console.log(msg1); // 'Hello Geoffrey'
But if you don't know name1
when you create msg1
.
For exemple if msg1
came from an API.
You can use :
let name2 = 'Geoffrey';
let msg2 = 'Hello ${name2}';
console.log(msg2); // 'Hello ${name2}'
const regexp = /\${([^{]+)}/g;
let result = msg2.replace(regexp, function(ignore, key){
return eval(key);
});
console.log(result); // 'Hello Geoffrey'
It will replace ${name2}
with his value.
Solution 9 - Javascript
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"
Solution 10 - Javascript
If you're trying to do interpolation for microtemplating, I like Mustache.js for that purpose.
Solution 11 - Javascript
Don't see any external libraries mentioned here, but Lodash has _.template()
,
https://lodash.com/docs/4.17.10#template
If you're already making use of the library it's worth checking out, and if you're not making use of Lodash you can always cherry pick methods from npm npm install lodash.template
so you can cut down overhead.
Simplest form -
var compiled = _.template('hello <%= user %>!');
compiled({ 'user': 'fred' });
// => 'hello fred!'
There are a bunch of configuration options also -
_.templateSettings.interpolate = /{{([\s\S]+?)}}/g;
var compiled = _.template('hello {{ user }}!');
compiled({ 'user': 'mustache' });
// => 'hello mustache!'
I found custom delimiters most interesting.
Solution 12 - Javascript
Simply use:
var util = require('util');
var value = 15;
var s = util.format("The variable value is: %s", value)
Solution 13 - Javascript
String.prototype.interpole = function () {
var c=0, txt=this;
while (txt.search(/{var}/g) > 0){
txt = txt.replace(/{var}/, arguments[c]);
c++;
}
return txt;
}
Uso:
var hello = "foo";
var my_string = "I pity the {var}".interpole(hello);
//resultado "I pity the foo"
Solution 14 - Javascript
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'
Solution 15 - Javascript
Peace quote of 2020:
Console.WriteLine("I {0} JavaScript!", ">:D<");
console.log(`I ${'>:D<'} C#`)
Solution 16 - Javascript
var hello = "foo";
var my_string ="I pity the";
console.log(my_string, hello)