Create a string of variable length, filled with a repeated character

Give this a try :P

s = '#'.repeat(10)

document.body.innerHTML = s

ES2015 the easiest way is to do something like

'X'.repeat(data.length)

X being any string, data.length being the desired length.

see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat

The best way to do this (that I've seen) is

var str = new Array(len + 1).join( character );

That creates an array with the given length, and then joins it with the given string to repeat. The .join() function honors the array length regardless of whether the elements have values assigned, and undefined values are rendered as empty strings.

You have to add 1 to the desired length because the separator string goes between the array elements.