[Solved-5 Solutions] Check does an object has property in JavaScript - javascript tutorial
Problem:
How to check if an object has a property in JavaScript ?
Solution 1:
The hasOwnProperty() method returns a boolean whether the object has the specified property as its own property to be indicated.
const object2 = new Object();
object2.property2 = 25;
console.log(object2.hasOwnProperty('property2'));
// expected output: true
console.log(object2.hasOwnProperty('toString'));
// expected output: false
console.log(object2.hasOwnProperty('hasOwnProperty'));
// expected output: false
true
false
false
Solution 2:
You can use this solution:
var obj = {
a: undefined,
b: null,
c: false
};
// a, b, c all found
for ( var prop in obj ) {
document.writeln( "Object1: " + prop );
}
function Class(){
this.a = undefined;
this.b = null;
this.c = false;
}
Class.prototype = {
a: undefined,
b: true,
c: true,
d: true,
e: true
};
var obj2 = new Class();
// a, b, c, d, e found
for ( var prop in obj2 ) {
document.writeln( "Object2: " + prop );
}
function hasOwnProperty(obj, prop) {
var proto = obj.__proto__ || obj.constructor.prototype;
return (prop in obj) &&
(!(prop in proto) || proto[prop] !== obj[prop]);
}
if ( Object.prototype.hasOwnProperty ) {
var hasOwnProperty = function(obj, prop) {
return obj.hasOwnProperty(prop);
}
}
// a, b, c found in modern browsers
// b, c found in Safari 2.0.1 and older
for ( var prop in obj2 ) {
if ( hasOwnProperty(obj2, prop) ) {
document.writeln( "Object2 w/ hasOwn: " + prop );
}
}
Solution 3:
Use Underscore.js
_.has(x, 'key');Which calls Object.prototype.hasOwnProperty, but- It is shorter to type
- Uses "a safe reference to
hasOwnProperty" (i.e. it works even if hasOwnProperty is overwritten).
function has(object, key) {
return object ? hasOwnProperty.call(object, key) : false;
}
// hasOwnProperty = Object.prototype.hasOwnProperty
Solution 4:
if (typeof(x.attribute) !== 'undefined')
A common alternative is to ensure that undefined is actually undefined, e.g. by putting the code into a function which accepts an additional parameter, called undefined, that isn’t passed a value.
(function (undefined) {
… your code …
if (x.attribute !== undefined)
… mode code …
})();
Solution 5:
var x = {'key': 1};
if ('key' in x) {
console.log('has');
}