javascript check if dictionary

Question

I have a simple program like:

var a = {\'a\': 1, \'b\': 2}
console.log(a)
console.log(a instanceof Array)
console.log(a.constructor instanceof Array)
         


        

Answer 1

The structure {'a': 1, 'b': 2} is a Javascript object. It can be used sort of like a dictionary, but Javascript does not have an actual dictionary type.

console.log(typeof a);            // "object"
console.log(Array.isArray(a));    // false, because it's not an array

If you want to know if something is an array, then use:

Array.isArray(a)

If you want to know if something is an object, then use:

typeof a === "object"

But, you will have to be careful because an Array is an object too.

---

If you want to know if something is a plain object, you can look at what jQuery does to detect a plain object:

isPlainObject: function( obj ) {
    // Not plain objects:
    // - Any object or value whose internal [[Class]] property is not "[object Object]"
    // - DOM nodes
    // - window
    if ( jQuery.type( obj ) !== "object" || obj.nodeType || jQuery.isWindow( obj ) ) {
        return false;
    }

    // Support: Firefox <20
    // The try/catch suppresses exceptions thrown when attempting to access
    // the "constructor" property of certain host objects, ie. |window.location|
    // https://bugzilla.mozilla.org/show_bug.cgi?id=814622
    try {
        if ( obj.constructor &&
                !hasOwn.call( obj.constructor.prototype, "isPrototypeOf" ) ) {
            return false;
        }
    } catch ( e ) {
        return false;
    }

    // If the function hasn't returned already, we're confident that
    // |obj| is a plain object, created by {} or constructed with new Object
    return true;
},