Question

I defined a prototype function ‘isElement’ of Node and I want to make it works like ‘div.isElement’ return ‘true’.

<div id="dom1">someText
    <p>This is p1 of <span class="bold">dom1</span></p>
</div>

Node.prototype.isElement = (function(){
    var result;
    var fn = function(){
        console.log(obj);
        result = (this.nodeType == 1 ? true : false);
        return result;
    };
    fn.toString = fn.valueOf = function(){
        return result;
    };
    return fn;
})();

var dom1 = document.getElementById('dom1');
dom1.isElement();  //true
dom1.isElement;  //true

If the ‘dom1’ never call the function ‘isElement()’,then ‘dom1.isElement’ return ‘undefined’. I understand why it return ‘undefined’,but I want to know how to makes it return ‘true’ or ‘false’ when ‘isElement()’ never be called.

I just want to use it like:

if(dom1.isElement){//do something}

but not like:

if(dom1.isElement()){//do something}

waiting for answers , thanks.

Answer 1

You can add a property that has your function as the getter:

Object.defineProperty(Node.prototype, "isElement", {
    get: function() {
        var result = this.nodeType == 1;
        return result;
    }
});