Question

So, my question has been asked by someone else in it’s Java form here: Java – Create a new String instance with specified length and filled with specific character. Best solution?

. . . but I’m looking for its JavaScript equivalent.

Basically, I’m wanting to dynamically fill text fields with “#” characters, based on the “maxlength” attribute of each field. So, if an input has has maxlength="3", then the field would be filled with “###”.

Ideally there would be something like the Java StringUtils.repeat("#", 10);, but, so far, the best option that I can think of is to loop through and append the “#” characters, one at a time, until the max length is reached. I can’t shake the feeling that there is a more efficient way to do it than that.

Any ideas?

FYI – I can’t simply set a default value in the input, because the “#” characters need to clear on focus, and, if the user didn’t enter a value, will need to be “refilled” on blur. It’s the “refill” step that I’m concerned with

Answer 1

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.