How to check for string having only spaces in javascript

Could look like

if( !currentValue.trim().length ) {
    // only white-spaces
}

docs: trim

Even if its very self-explanatory; The string referenced by currentValue gets trimmed, which basically means all white-space characters at the beginning and the end will get removed. If the entire string consists of white-space characters, it gets cleaned up alltogether, that in turn means the length of the result is 0 and !0 will be true.

About performance, I compared this solution vs. the RegExp way from @mishik. As it turns out, .trim() is much faster in FireFox whereas RegExp seems way faster in Chrome.

http://jsperf.com/regexp-vs-trim-performance

Simply:

if (/^\s*$/.test(your_string)) {
  // Only spaces
}

To match space only:

if (/^ *$/.test(your_string)) {
  // Only spaces
}

Explanation: /^\s*$/ - match a beginning of a string, then any number of whitespaces (space, newline, tab, etc...), then end of string. /^ *$/ - same, but only for spaces.

If you do not want to match empty string: replace * with + to make sure that at least one character is present.