Type Checking in JavaScript

Publish Date: Oct 18 '20

5 0

I like to group all type checking tasks into helper functions like this to be used internally. This has the advantage in case of code minification ¹

function isArray(x) {
    return Array.isArray(x);
}

function isBoolean(x) {
    return false === x || true === x;
}

function isElement(x) {
    return x instanceof Element;
}

function isFloat(x) {
    return isNumber(x) && 0 !== x % 1;
}

function isFunction(x) {
    return 'function' === typeof x;
}

function isInteger(x) {
    return isNumber(x) && 0 === x % 1;
}

function isNull(x) {
    return null === x;
}

function isNumber(x) {
    return 'number' === typeof x;
}

function isNumeric(x) {
    return /^-?(?:\d*\.)?\d+$/.test(x + "");
}

function isObject(x, isPlainObject) {
    if ('object' !== typeof x) {
        return false;
    }
    return isPlainObject ? x instanceof Object : true;
}

function isPattern(x) {
    return x instanceof RegExp;
}

function isSet(x) {
    return 'undefined' !== typeof x && null !== x;
}

function isString(x) {
    return 'string' === typeof x;
}

These functions are very inspired by PHP which already has standard functions such as is_array(), is_object(), is_string(), etc.

There was a proposal to allow users to write the type checking as if ($int instanceof int) {} expression somewhere. I don’t know where the page is. I couldn’t find it anymore.

Update: found it!

Update: Is now available as Node.js module.

taufik-nurrohman / is