how to do overloading in javascript?

This question already has an answer here:

Function overloading in Javascript - Best practices 29 answers

---

在调用函数时，JavaScript不要求传递所有参数，因此可以像这样实现重载：

function foo(a, b, c) {
    if (c === undefined) {
        if (b === undefined) {
            if (a === undefined) console.log("zero argument pass");
            else console.log("one argument pass");
        }
        else console.log('two argument pass');
    }
    else console.log('three argument pass');
}

---

从http://ejohn.org/blog/javascript-method-overloading/

var namespace = {};

function addMethod(object, name, fn) {
    var old = object[name];
    object[name] = function() {
        if (fn.length === arguments.length) {
            return fn.apply(this, arguments);
        } else if (typeof old === 'function') {
            return old.apply(this, arguments);
        }
    };
}

addMethod(namespace, "foo", function (a) {
    console.log("one argument pass");
});

addMethod(namespace, "foo", function (a, b) {
    console.log("two arguments pass");
});

addMethod(namespace, "foo", function (a, b, c) {
    console.log("three argument pass");
});

namespace.foo(1);
namespace.foo(1, 2);
namespace.foo(1, 2, 3);

var namespace = {};

function addMethod(object, name, fn) {
    var old = object[name];
    object[name] = function() {
        if (fn.length === arguments.length) {
            return fn.apply(this, arguments);
        } else if (typeof old === 'function') {
            return old.apply(this, arguments);
        }
    };
}

addMethod(namespace, "foo", function (a) {
    document.write("one argument pass<br/>");
});

addMethod(namespace, "foo", function (a, b) {
    document.write("two arguments pass<br/>");
});

addMethod(namespace, "foo", function (a, b, c) {
    document.write("three argument pass<br/>");
});

namespace.foo(1);
namespace.foo(1, 2);
namespace.foo(1, 2, 3);

---

Check the arity

function foo(a, b, opts) {
    if (arguments.length === 1) {
        console.log("one argument pass")
    } else if (arguments.length === 2) {
        console.log("two argument pass")
    } else if (arguments.length === 3) {
        console.log("three argument pass")
    }
}

foo(1); // "one argument pass"
foo(1,2); // "two argument pass"
foo(1,2,3); // "three argument pass"

http://jsfiddle.net/moogs/m84fg8ac/2/

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