The following in a Javascript console:
var a = {'foo': []};
var b = {};
for (var key in a) {
b[key] = a[key];
}
a['foo'].push(1);
console.log(b);
Yields:
Object foo=[1]
I want to make a copy by value in b of each array for each key in a. Is there an easier way?
You could make a "clone" function that creates a new object, based on the original object constructor, and then clone that original object properties also if they are objects:
function clone(obj){
if(typeof(obj) != 'object' && obj != null)
return obj; // return the value itself if isn't an object
// or null, since typeof null == 'object';
var temp = new obj.constructor();
for(var key in obj)
temp[key] = clone(obj[key]);
return temp;
}
var a = {'foo': []};
var b = clone(a);
a['foo'].push(1);
console.log(b); // Object foo=[0]
Object.prototype.foo = function () {}; will create infinite recursion.
obj.constructor() is going to die on constructor functions (temp will be undefined), and potentially clobber globals.new operator while I think on something better...This is called Deep Copy. You can find examples in:
Easier way:
var a = {'foo': []};
var b = a;
a['foo'].push(1);
console.log(b);
Output is the same.
Edit:
var a = {'foo': []};
var b = {};
for (var key in a) {
if (a.hasOwnProperty(key)) {
b[key] = [];
for (var i = 0; i < a[key].length; i += 1) {
b[key][i] = a[key][i];
}
}
}
a['foo'].push(1);
console.log(b);
a[key].slice(0).As this will add support for deep-copying arrays in your code:
var a = {'foo': []};
var b = {};
for (var key in a) {
if (Object.prototype.toString.call(b[key]) === "[object Array]") {
b[key] = a[key].slice(0);
} else {
b[key] = a[key];
}
}
a['foo'].push(1);
console.log(b);
console.logfunction to work.