Question

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javascript – Array.map and parseInt

I saw this example of strange JavaScript behavior on twitter

['10','10','10','10','10'].map(parseInt)

evaluates to

[10, NaN, 2, 3, 4]

could somebody explain this behavior? I verified it in chrome and firebug

['10','10','10','10','10'].map(function(x){return parseInt(x);})

correctly returns an array of 10s as integers. Is this an improper use of map(), a bug with parseInt, or something else?

Answer 1

parseInt receives two arguments: string and radix:

var intValue = parseInt(string[, radix]);

while map handler’s second argument is index:

… callback is invoked with three arguments: the value of the element,
the index of the element, and the Array object being traversed.