Javascript Empty String vs (null and undefined)

Question

I have a object

var data = {1:undefined,2:null,3:10,4:""}

I want to replace all the undefined and null values by 0. I am using the following code to do that:

for (var index in data) {
    if (!data[index]) {
        data[index] = 0;
    }
}

Result I am expecting is : {1:0,2:0,3:10:4:""} But Result is : {1:0,2:0,3:10:4:0} because it is considering empty string as null. Is it known behavior ?

I can check it by using (if(data[index] == undefined || data[index] == null)) But I wanted to know the behavior of the above solution.

[yes](https://developer.mozilla.org/en-US/docs/Glossary/Falsy). — Nina Scholz, May 18 '16 at 11:10

score 1 · Answer 1 · answered May 18 '16 at 11:10

1

You can add typeof data[index] != 'string'

var data = {1:undefined,2:null,3:10,4:""}

for (var index in data) {
  if (!data[index] && typeof data[index] != 'string') {
    data[index] = 0;
  }
}

console.log(data)

answered May 18 '16 at 11:10

Nenad Vracar

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score 1 · Answer 2 · answered May 18 '16 at 11:12

1

This is because a string of length 0 is "falsy", which means that it, if evaluated as a boolean, will translate to false. Read more on "falsy" over here. You can fix your code in the following way:

for (var index in data) {
    if (typeof data[index] == "undefined" || data[index] == null) {
        data[index] = 0;
    }
}

answered May 18 '16 at 11:12

Michaël van de Weerd

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Thanks @Michaël for useful link. – Bhuneshwer May 18 '16 at 11:18

score 0 · Answer 3 · answered May 18 '16 at 11:11

0

Try:

if ((typeof <your variable> == "undefined") ||
    (       <your variable> == ""         )    ) {
    <your variable> = 0 ;
}

By the way, Are you using "1", "2" indices?

answered May 18 '16 at 11:11

FDavidov

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Javascript Empty String vs (null and undefined)

3 Answers3