ECMAScript 5 has the filter()
prototype for Array
types, but not Object
types, if I understand correctly.
How would I implement a filter()
for Object
s in JavaScript?
Let's say I have this object:
var foo = {
bar: "Yes"
};
And I want to write a filter()
that works on Object
s:
Object.prototype.filter = function(predicate) {
var result = {};
for (key in this) {
if (this.hasOwnProperty(key) && !predicate(this[key])) {
result[key] = this[key];
}
}
return result;
};
This works when I use it in the following demo, but when I add it to my site that uses jQuery 1.5 and jQuery UI 1.8.9, I get JavaScript errors in FireBug.
Object.prototype.filter = function(predicate) {
var result = {};
for (key in this) {
if (this.hasOwnProperty(key) && !predicate(this[key])) {
console.log("copying");
result[key] = this[key];
}
}
return result;
};
var foo = {
bar: "Yes",
moo: undefined
};
foo = foo.filter(function(property) {
return typeof property === "undefined";
});
document.getElementById('disp').innerHTML = JSON.stringify(foo, undefined, ' ');
console.log(foo);
#disp {
white-space: pre;
font-family: monospace
}
<div id="disp"></div>
Never ever extend Object.prototype
.
Horrible things will happen to your code. Things will break. You're extending all object types, including object literals.
Here's a quick example you can try:
// Extend Object.prototype
Object.prototype.extended = "I'm everywhere!";
// See the result
alert( {}.extended ); // "I'm everywhere!"
alert( [].extended ); // "I'm everywhere!"
alert( new Date().extended ); // "I'm everywhere!"
alert( 3..extended ); // "I'm everywhere!"
alert( true.extended ); // "I'm everywhere!"
alert( "here?".extended ); // "I'm everywhere!"
Instead create a function that you pass the object.
Object.filter = function( obj, predicate) {
let result = {}, key;
for (key in obj) {
if (obj.hasOwnProperty(key) && !predicate(obj[key])) {
result[key] = obj[key];
}
}
return result;
};