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(Fake) Operator Overloading

Because Javascript will call the .valueOf method for an object to coerce the value before applying most operators (like basic math ops, binary ops, comparison ops), you can get tricky and change the value returned on the left to the result of a different operation.

    var obj1 = {
        valueOf: function () {
            console.log("valueOf1");
            return 1;
        }
    };
    var obj2 = {
        valueOf: function () {
            console.log("valueOf2");
            return 2;
        }
    };

And now:
obj1 + obj2
    valueOf1
    valueOf2
    3
Because these are called in order, obj1 can set a flag in the prototype and also store it's value in the prototype, but return nothing. Then obj2 will know it's not first, and can do the actual operation, and return the desired complete value, using obj1's value and it's own.
+

Code:

See also:


file: /Techref/language/java/script/operator-overloading.htm, 4KB, , updated: 2023/5/11 21:41, local time: 2023/12/3 22:50, owner: JMN-EFP-786,
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