JavaScript - String concat() method example

Concat method is used to join two or more strings in JavaScript. The method appends passed arguments to right side of string. 

// ONLINE-RUNNER:browser;

var a = 'abc';
var b = '123';

console.log( a.concat()  ); // abc
console.log( a.concat(b) ); // abc123
console.log( b.concat(a) ); // 123abc

1. Documentation

2. Alternative concatenation approach example

Note: it is strongly recommended to use += operator instead concat() method to get better peformance of operations.

// ONLINE-RUNNER:browser;

var text = '_abc';

text += '_123';
text += '_ABC';
text += '_000';

console.log(text);

3. Concatenation performance example

In this section presented program execution time depends of JavaScript implementation.

Note: some browsers can be optimized with concat() method.

// ONLINE-RUNNER:browser;

var text1 = 'abc1';
var text2 = 'abc1';

var texts = [
    'abc2', 'abc3', 'abc4'
];

// -----------------------------------------------
// += operator test

var t1 = new Date();

for (var i = 0; i < 100000; ++i) {
    text1 += texts[i % texts.length];
}

var t2 = new Date();
var dt = t2 - t1;

console.log(dt + 'ms  <- += operator test time');

// -----------------------------------------------
// concat method test

var t1 = new Date();

for (var i = 0; i < 100000; ++i) {
    text2 = text2.concat(texts[i % texts.length]);
}

var t2 = new Date();
var dt = t2 - t1;

console.log(dt + 'ms  <- concat method test time');