使用默认函数扩展JavaScript对象

Question

In google app scripts I have a one dimensional data array that I can get values from like this:

data[0]

I'd love to be able to pass in the column name instead like this:

data("A")

That way I don't have to convert letters into their array position. So I'd like to extend the array object (extending isn't really risky since it's running in an isolated script environment).

I know I can add a function to the array prototype using this letter to number function and this object extension question like this:

 Array.prototype.byCol = function(colName) { return this[getColumnNumber(colName) - 1]; } function getColumnNumber(str) { var out = 0, len = str.length; for (pos = 0; pos < len; pos++) { out += (str.charCodeAt(pos) - 64) * Math.pow(26, len - pos - 1); } return out; } var data = [1,2,3,4]; document.write(data.byCol("B")); 

But this is a slightly bulkier calling syntax than I wanted.

Based on this question on default functions , it looks like it's possible to assign a default function to an object, but they're doing so by just creating a function object like this:

var test = new func(function() {
    // do something
});

Can I get extend the array so that it will execute a default function when called as a method?

Answer 1

Put simply, you can't make something into a function if it's not already a function, and you can't really extend arrays.

What you can do is create a wrapper function that wraps an array and provides the functionality you want, and also include the ability to get back the original array if you need it:

 var wrapper = (function() { function getColumnNumber(str) { return Array.prototype.reduce.call(str.toUpperCase(), function (t, c) { return 26 * t + c.charCodeAt(0) - 64; }, 0) - 1; } return function(arr) { return function(col, val) { if (arguments.length === 0) { return arr; } if (arguments.length > 1) { arr[getColumnNumber(col)] = val; } return arr[getColumnNumber(col)]; }; }; })(); var w = wrapper([10, 20, 30, 40, 50]); snippet.log(w('D')); // 40 w('D', 33); // set value snippet.log(w('D')); // 33 w()[3] = 42; // access underlying array directly w().push(60); snippet.log(w('D')); // 42 snippet.log(w('F')); // 60 

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