How to build/concatenate strings in JavaScript?

Question

Does JavaScript support replacement/interpolation?

Overview

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I'm working on a JavaScript project and as it gets bigger it's getting harder and harder to keep the strings in good shape. I would like to know what is the simplest and most traditional way to construct or build a string in JavaScript.

My experience so far:

As projects become more complex, string concatenation starts to look ugly and becomes harder to maintain.

The most important thing at this point is simplicity and readability, think about a bunch of moving parts, not just 2-3 variables.

Equally important, it is currently supported by major browsers (i.e. at least ES5).

I know the JavaScript connection abbreviation:

var x = 'Hello';
var y = 'world';
console.log(x ', ' y);

There is also the String.concat function.

I'm looking for something cleaner.

Ruby and Swift do this in an interesting way.

Ruby

var x = 'Hello'
var y = 'world'
print "#{x}, #{y}"

Swift

var x = "Hello"
var y = "world"
println("(x), (y)")

I thought there might be something similar in JavaScript, maybe something like sprintf.js.

Question

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Can this be done without a third-party library? If not, what can I use?

Answer 1

I'm disappointed that no one in the other answers explained "best way" to mean "fastest way"...

I extracted two examples from here and added str. join() and str.reduce() from nishanths' answer above. Here are my results on Firefox 77.0.1 on Linux.

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Note: I discovered while testing these that if I put str = str.concat() and str = directly before or after each other Between them, the second one always performs better... so I run these tests individually and comment on the results of the other tests...

Even so, their speeds would change a lot if I reran them, so I measured each 3 times.

1 character at a time:

• str = str.concat(): 841, 439, 956 ms / 1e7
of concat()
• ............str =:949, 1130, 664 milliseconds / 1e7 ='s
• ......[].join(): There are 3350, 2911, 3522 ms / 1e7 characters in []
• ...[].reduce(): 3954, 4228, 4547 ms / 1e7 characters in []

26 strings at a time:

• str = str.concat(): 444, 744, 479 ms / 1e7
of concat()
• ............str =：1037, 473, 875 milliseconds / 1e7 ='s
• ........[].join(): 2693, 3394, 3457 ms / 1e7 string in []
• ......[].reduce(): 2782, 2770, 4520 ms / 1e7 string in []

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So, whether appending 1 character at a time or appending 26 strings at a time:

• Clear winner: basically a tie between str = str.concat() and str =
• Obvious losers: [].reduce(), then [].join()

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My code, easy to run in browser console:

{
  console.clear();

  let concatMe = 'a';
  //let concatMe = 'abcdefghijklmnopqrstuvwxyz';

  //[].join()
  {
    s = performance.now();
    let str = '', sArr = [];
    for (let i = 1e7; i > 0; --i) {
      sArr[i] = concatMe;
    }
    str = sArr.join('');
    e = performance.now();
    console.log(e - s);
    console.log('[].join(): ' + str);
  }

  //str +=
  {
    s = performance.now();
    let str = '';
    for (let i = 1e7; i > 0; --i) {
      str += concatMe;
    }
    e = performance.now();
    console.log(e - s);
    console.log('str +=: ' + str);
  }

  //[].reduce()
  {
    s = performance.now();
    let str = '', sArr = [];
    for (let i = 1e7; i > 0; --i) {
      sArr[i] = concatMe;
    }
    str = sArr.reduce(function(pre, next) {
      return pre + next;
    });
    e = performance.now();
    console.log(e - s);
    console.log('[].reduce(): ' + str);
  }

  //str = str.concat()
  {
    s = performance.now();
    let str = '';
    for (let i = 1e7; i > 0; --i) {
      str = str.concat(concatMe);
    }
    e = performance.now();
    console.log(e - s);
    console.log('str = str.concat(): ' + str);
  }

  'Done';
}

Answer 2

Using ES6, you can use

• Template string:

  var username = 'craig';
  console.log(`hello ${username}`);

ES5 and below:

• Using Operator

  var username = 'craig';
  var joined = 'hello ' + username;

• String concat (..)

  var username = 'craig';
  var joined = 'hello '.concat(username);

Or, use the array method:

• join( ..)：

  var username = 'craig';
  var joined = ['hello', username].join(' ');

• Or more exotically, < code>reduce(..) combined with any of the above:

  var a = ['hello', 'world', 'and', 'the', 'milky', 'way'];
  var b = a.reduce(function(pre, next) {
    return pre + ' ' + next;
  });
  console.log(b); // hello world and the milky way