Using Array.map() in conjuction with parseInt gives unexpected results

Question

I have the following JS Problem. If i try to convert an array of strings using the parseInt function as a mapped function with the Array.map method, i experienced this strange result. What is wrong here?

console.log(['1','1'].map(parseInt))

Returns a strange Array containing the following:

[1, NaN]

Is parseInt not a regular function?

score 3 · Answer 1 · answered Sep 30 '14 at 18:41

3

parseInt takes multiple parameters. Array.map is run with multiple parameters.

to avoid side effects, you can run it like this:

console.log(['1','1'].map(function(item){
    return parseInt(item);
}))

answered Sep 30 '14 at 18:41

Madd0g

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...and it's even readable IMHO – Zoltán Tamási Sep 30 '14 at 18:42

score 1 · Accepted Answer · answered Sep 30 '14 at 18:43

Right, parseInt is not a regular function. It takes 2 arguments. The first is the number to parse, the second is the radix. Array.map passes 3 - the value, index, and full array.

Each call goes like this:

 parseInt('1', 0) // 1
 parseInt('1', 1) // NaN

To fix this, you need to manually call the function.

console.log(['1','1'].map(function(num){
    return parseInt(num);
}));

Using Array.map() in conjuction with parseInt gives unexpected results

2 Answers2