Question

I’m looking for a cross-browser-compliant Javascript equivalent to Rails’ Object.blank? (and its counterpart, Object.present?) that returns true for empty objects, empty arrays, empty strings, and null and undefined values. Has anyone seen such a thing? I could write it myself but I know there are some IE gotchas and I figure someone else has probably already tackled this.

Answer 1

I just whipped this together. Have not testing it on any browsers, just ran it in Node.js. But I think it should work.

function blank(obj) { 
    var cache;

    if((cache = typeof obj) !== 'boolean' && (cache !== 'number' || isNaN(obj)) && !obj)
        return true;
    if(cache == 'string' && obj.replace(/\s/g, '').length === 0)
        return true;
    if(cache == 'object') {
        if((cache = toString.call(obj)) == '[object Array]' && obj.length === 0)
            return true;
        if(cache == '[object Object]') {
            for(cache in obj) {
                return false;
            }
            return true;
        }
    }

    return false;
}

So…

blank([])
// true
blank({})
// true
blank({ x: 123 })
// false
blank('')
// true
blank(' ')
// true
blank(' asdf')
// false
blank()
// true
var x; blank(x)
// true
var x = 12; blank(x)
// false
blank(true)
// false
blank(false)
// false
blank(0)
// false
blank(NaN)
// true

edit: added a catch so that true and false come back as not blank. If you want false to be considered blank then change that.

edit 2: last change! preventing blank(0) from returning true. But allowing NaN to be considered blank.