1. String slice() method example

This approach allows to get substring by using negative indexes.

So by using 0 and  -3 indexes as range we get <0, text.length - 3> text range.  

var text = 'abcde';
var substring = text.slice(0, -3);

console.log(substring); // ab

2. String substring() method example

This is alternative approach to slice method based solution.

var text = 'abcde';
var substring = text.substring(0, text.length - 3);

console.log(substring); // ab

3. String replace() method example

There is another trick that allows to replace all characters that match rexpression condition.

By using .{0,3}$ pattern we match all any 3 characters (up to 3 characters) that are loacated at the end of string.

var text = 'abcde';
var substring = text.replace(/.{0,3}$/, '');

console.log(substring); // ab