Repeat String - Javascript

brad_208 0
Viewed 153441

What is the best or most concise method for returning a string repeated an arbitrary amount of times?

The following is my best shot so far:

function repeat(s, n){
    var a = [];
    while(a.length < n){
        a.push(s);
    }
    return a.join('');
}
javascript string
30 Answers

Note to new readers: This answer is old and and not terribly practical - it's just "clever" because it uses Array stuff to get String things done. When I wrote "less process" I definitely meant "less code" because, as others have noted in subsequent answers, it performs like a pig. So don't use it if speed matters to you.

I'd put this function onto the String object directly. Instead of creating an array, filling it, and joining it with an empty char, just create an array of the proper length, and join it with your desired string. Same result, less process!

String.prototype.repeat = function( num )
{
    return new Array( num + 1 ).join( this );
}

alert( "string to repeat\n".repeat( 4 ) );
user_88150

Expanding P.Bailey's solution:

String.prototype.repeat = function(num) {
    return new Array(isNaN(num)? 1 : ++num).join(this);
    }

This way you should be safe from unexpected argument types:

var foo = 'bar';
alert(foo.repeat(3));              // Will work, "barbarbar"
alert(foo.repeat('3'));            // Same as above
alert(foo.repeat(true));           // Same as foo.repeat(1)

alert(foo.repeat(0));              // This and all the following return an empty
alert(foo.repeat(false));          // string while not causing an exception
alert(foo.repeat(null));
alert(foo.repeat(undefined));
alert(foo.repeat({}));             // Object
alert(foo.repeat(function () {})); // Function

EDIT: Credits to jerone for his elegant ++num idea!

user_2923820

Here's the JSLint safe version

String.prototype.repeat = function (num) {
  var a = [];
  a.length = num << 0 + 1;
  return a.join(this);
};
Admin1 
function repeat(s, n) { var r=""; for (var a=0;a<n;a++) r+=s; return r;}
Joel_Coehoorn_30430

With ES8 you could also use padStart or padEnd for this. eg.

var str = 'cat';
var num = 23;
var size = str.length * num;
"".padStart(size, str) // outputs: 'catcatcatcatcatcatcatcatcatcatcatcatcatcatcatcatcatcatcatcatcatcatcat'
user_71444270

To repeat a string in a specified number of times, we can use the built-in repeat() method in JavaScript.

Here is an example that repeats the following string for 4 times:

const name = "king";

const repeat = name.repeat(4);

console.log(repeat);

Output:

"kingkingkingking"

or we can create our own verison of repeat() function like this:

function repeat(str, n) {
  if (!str || !n) {
    return;
  }

 let final = "";
  while (n) {
    final += s;
    n--;
  }
  return final;
}

console.log(repeat("king", 3))

(originally posted at https://reactgo.com/javascript-repeat-string/)

user_92786450
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