javascript - Cannot read property 'forEach' of undefined in reactjs application - Stack Overflow

admin管理员组

文章数量:1426929

I have a JS method that takes a JSON file and try to get information out of it:

getData(json) {
        var output = '';

        json.Legs.forEach(function (item) {
            .
            .
            .
            .
            .
            .
        });

        return output;
    }

I am getting this error for forEach:

Uncaught TypeError: Cannot read property 'forEach' of undefined

Is it possible to use forEach like this or I shouldn't be using forEach at all? Is there nother way to do this?

I have a JS method that takes a JSON file and try to get information out of it:

getData(json) {
        var output = '';

        json.Legs.forEach(function (item) {
            .
            .
            .
            .
            .
            .
        });

        return output;
    }

I am getting this error for forEach:

Uncaught TypeError: Cannot read property 'forEach' of undefined

Is it possible to use forEach like this or I shouldn't be using forEach at all? Is there nother way to do this?

• javascript
• json
• foreach

Share Improve this question Follow asked Feb 6, 2018 at 8:41 karan kalimikaran kalimi 2311 gold badge11 silver badge1010 bronze badges 3

• 2 error is pretty much clear, you do not have data within json.Legs. – Jigar Shah Commented Feb 6, 2018 at 8:43
• JSON by definition does not have arbitrary properties as it is just a string. Do you mean a JavaScript object instead or do you pass a string? How do you call that function? – str Commented Feb 6, 2018 at 8:44
• You need to run each loop after checking only if json.Legs is not null. e.g if(!json.Legs){ json.Legs.forEach(function (item) { . . . . . . }); } – Abdul Qayyum Commented Feb 6, 2018 at 8:45

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 2

You need to execute loop after confirming that json.Legs is not null. e.g

if(json.Legs){
  json.Legs.forEach(function (item) {
            .
            .
            .
            .
            .
            .
        });
}

Add this as the first line in the code and see what it prints. If it is an array you can all forEach on it. Otherwise it's throwing the right error.

console.log(json.Legs)

Something like this should do the trick (check whether .legs property exists and whether its an array before iterating):

getData(json) {
    var output = '';

    if(json.Legs && Array.isArray(json.Legs)){

     json.Legs.forEach(function (item) {
        //do something with item
     });
    }

    return output;
}

本文标签： javascriptCannot read property 39forEach39 of undefined in reactjs applicationStack Overflow