SiddharthThe typeof operator is a really useful one but it has a few pitfalls:
typeof ["an", "array"] // object
typeof /regex/g // object
typeof null // object
typeof NaN // number
typeof Number('I am not a number!') // number
Ok, that's a lot of pitfalls;
But there is a way to get more detailed types using Object.prototype.toString.call() on a value:
// This statement basically means: "Call the toString method of the object prototype on whatever value you like"
Object.prototype.toString.call({ object: "true" }) // the infamous [object Object]
Object.prototype.toString.call(["an", "array"]) // [object Array]
Object.prototype.toString.call("a string") // [object String]
Object.prototype.toString.call(1n) // [object Bigint]
Object.prototype.toString.call(new Date()) // [object Date] really
Object.prototype.toString.call(new Error("an error")) // [object Error]
Object.prototype.toString.call(function () {}) // [object Function]
Object.prototype.toString.call(function* () {}) // [object GeneratorFunction]
Object.prototype.toString.call(/regex/gi) // [object RegExp]
Object.prototype.toString.call(Symbol()) // [object Symbol]
Object.prototype.toString.call(NaN) // it's not perfect: [object Number]
Of course, this could be made a function (with a few finishing touches from here)
function type(obj, showFullClass) {
// Whether to return the whole type
if (showFullClass && typeof obj === "object") {
return Object.prototype.toString.call(obj);
}
if (obj == null) { return (obj + '').toLowerCase(); } // implicit toString() conversion
// Removed, see comments
// if (isNaN(+obj)) return "nan";
if (Object.is(obj, NaN)) return "nan";
var deepType = Object.prototype.toString.call(obj).slice(8,-1).toLowerCase();
if (deepType === 'generatorfunction') { return 'function' }
// Prevent overspecificity (for example, [object HTMLDivElement], etc).
// Account for functionish Regexp (Android <=2.3), functionish <object> element (Chrome <=57, Firefox <=52), etc.
// String.prototype.match is universally supported.
return deepType.match(/^(array|bigint|date|error|function|generator|regexp|symbol)$/) ? deepType :
(typeof obj === 'object' || typeof obj === 'function') ? 'object' : typeof obj;
}
