How to remove the white space at the start of the string

This is what you want:

function ltrim(str) {
  if(!str) return str;
  return str.replace(/^\s+/g, '');
}

Also for ordinary trim in IE8+:

function trimStr(str) {
  if(!str) return str;
  return str.replace(/^\s+|\s+$/g, '');
}

And for trimming the right side:

function rtrim(str) {
  if(!str) return str;
  return str.replace(/\s+$/g, '');
}

Or as polyfill:

// for IE8
if (!String.prototype.trim)
{
    String.prototype.trim = function ()
    {
        // return this.replace(/^\s+|\s+$/g, '');
        return this.replace(/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g, '');
    };
}

if (!String.prototype.trimStart)
{
    String.prototype.trimStart = function ()
    {
        // return this.replace(/^\s+/g, '');
        return this.replace(/^[\s\uFEFF\xA0]+/g, '');
    };
}

if (!String.prototype.trimEnd)
{
    String.prototype.trimEnd = function ()
    {
        // return this.replace(/\s+$/g, '');
        return this.replace(/[\s\uFEFF\xA0]+$/g, '');
    };
}

Note:
\s: includes spaces, tabs \t, newlines \n and few other rare characters, such as \v, \f and \r.
\uFEFF: Unicode Character ‘ZERO WIDTH NO-BREAK SPACE’ (U+FEFF)
\xA0: ASCII 0xA0 (160: non-breaking space) is not recognised as a space character