Create string of Letter and length of a string

Question

I would like to create a string, from a letter and length of a string. This is what I currently have, but is there a better way to do this?

function generate(letter, len) {
   var str = '';
   for (var i=0; i<len; i++) {
     str+=letter;
   }
  
   return str;
  
}

I think questions like this belongs on codereview.stackexchange.com — Andreas Louv
– Andreas Louv, Commented Jun 3, 2015 at 13:46
Depends on the js environment (ES6 String.prototype.repeat), available libraries in the environment, what you mean by "better" — Xotic750
– Xotic750, Commented Jun 3, 2015 at 14:08

Amit Joki · Accepted Answer · 2015-06-03 13:57:06Z

4

Don't know if this is better in terms of performance as some engines optimize the code while others do not. However it's readable, to a javascript programmer.

You can create an array with size len + 1 and then join it by the letter.

For this, we will make use of array constructor, where we can define the size of the array and Array.join to join the array with the given letter.

function generate(letter, len) {
    return new Array(len + 1).join(letter); 
}

edited Jun 3, 2015 at 13:57

answered Jun 3, 2015 at 13:37

Amit Joki

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7 Comments

Andreas Louv Over a year ago

Why is this better? Is it faster? I doubt it. Is is easier to read? That can be discussed to infinity.

num8er Over a year ago

I think it's not better way to join probabily inifinite length of string. by creating array You're creating an object in ram, then You're joining it also consuming resources. Using "for loop" for generating is still better way.

Andreas Louv Over a year ago

@AmitJoki You don't know how the engine ( compiler / interpreter ) will handle sting concatenation. Maybe it will use something like the StringBuilder from Java or C#. Maybe it will reserve memory for each string and free it again after it's done being used.

Andreas Louv Over a year ago

Maybe it will inspect the code and make a string of length len and simply rewrite the concatenation to str[i] = letter.

Amit Joki Over a year ago

@dev-null jsperf.com/for-vs-array-join/3 For loop may be faster when the len is small..but what happens when it becomes somewhat big? Talk about micro-optimization

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