Push to a javascript array if it exists, if not then create it first - Stack Overflow

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Is there a way for this line to always work and not throw TypeError: Cannot read property 'Whatever' of undefined

var MyArray = [];
MyArray[StringVariableName][StringVariableName2].push("whatever");

Is there a way for this line to always work and not throw TypeError: Cannot read property 'Whatever' of undefined

var MyArray = [];
MyArray[StringVariableName][StringVariableName2].push("whatever");

• javascript
• arrays
• object

Share Improve this question Follow edited Feb 18, 2014 at 16:50 Sachin Jain 21.8k3434 gold badges110110 silver badges176176 bronze badges asked Feb 18, 2014 at 16:07 Nadav MillerNadav Miller 49122 gold badges55 silver badges1515 bronze badges 1

• 1 MyArray = MyArray || []; – Cory Danielson Commented Feb 18, 2014 at 16:15

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5 Answers 5

Sorted by: Reset to default 19

Try this:

var MyArray = [];
MyArray[StringVariableName] = MyArray[StringVariableName] || [];
MyArray[StringVariableName][StringVariableName2] = MyArray[StringVariableName][StringVariableName2] || [];
MyArray[StringVariableName][StringVariableName2].push("whatever");

You could even, through the power of expressions, do this with a one-liner.

(MyArray[StringVariableName][StringVariableName2] || (MyArray[StringVariableName][StringVariableName2] = [])).push("whatever");

You could use the literal syntax to set things up like you'd have them:

var myObj = {
    StringVariableName: {
        StringVariableName2: []
    }
};

myObj.StringVariableName.StringVariableName2.push("whatever");

I think instead of using array in the first place, use object if your keys are not integers. In Javascript Arrays are also object So it is not wrong to do this

var a = [];
a['key'] = 'something';

console.log(a); //Gives []

I think it is conceptually wrong So instead of using Array to hold such pair of data you should use objects. See this:

var myObject = myObject || {};
myObject[str1] = myObject[str1] || {};
myObject[str1][str2] = myObject[str][str2] || [];

// Now myObject[str1][str2] is an array. Do your original operation

myObject[str1][str2].push("whatever");

To check without getting an error:

this snippet allows you to check if a chained object exists.

var x;
try{x=MyArray[name1][name2][name3][name4]}catch(e){}
!x||(x.push('whatever'));

from

https://stackoverflow.com/a/21353032/2450730

Shorthand creation of object chains in Javascript

this function allows you to create chained objects with a simple string.

function def(a,b,c,d){
 c=b.split('.');
 d=c.shift();//add *1 for arrays
 a[d]||(a[d]={});//[] for arrays
 !(c.length>0)||def(a[d],c.join('.'));
}

usage

var MyArray={};//[]
def(MyArray,'name1.name2.name3.name4');//name1+'.'+name2....

from

https://stackoverflow.com/a/21384869/2450730

both work also for arrays with a simple change.replace {} with []

if you have any questions just ask.

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