Harmful mapping (extra args for parseInt)

map-parseInt.js

var a = ["1", "2", "3"];

// try to get mapped array
// containing numbers

console.log(a.map(parseInt)); // but get [1, NaN, NaN] !

// Explanation:

// per step 8.c.ii of the 15.4.4.9
// Array.prototype.map
// see: http://es5.github.com/#x15.4.4.19
// `mappedValue` of every call is taken as
// the result of the callback function,
// applied for three arguments: item, index and array.

// parseInt accepts an optional parameter - the radix
// 15.1.2.2 parseInt (string , radix)
// see: http://es5.github.com/#x15.1.2.2
// if radix is `undefined` or `0` it's assumed as `10`

// I.e.

var res = [];

res[0] = parseInt("1", 0, a); // 1, since radix is 0
res[1] = parseInt("2", 1, a); // NaN, 2 in radix 1?
res[2] = parseInt("3", 2, a); // NaN, 3 in radix 2?

console.log(res); // [1, NaN, NaN]

// see http://twitter.com/#!/awbjs/status/35759670580887552

// If strings are correct numbers, then Number
// function can be used for the case


console.log(a.map(Number)); // [1, 2, 3]

// see http://twitter.com/#!/angusTweets/status/35774944293953537