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");
5 Answers
Try this:
var MyArray = [];
MyArray[StringVariableName] = MyArray[StringVariableName] || [];
MyArray[StringVariableName][StringVariableName2] = MyArray[StringVariableName][StringVariableName2] || [];
MyArray[StringVariableName][StringVariableName2].push("whatever");
3 Comments
Nadav Miller
Works amazing, can you explain what that assignment means?
Sachin Jain
@NadavMiller It simply is a logical OR. If first part is true, second part is not executed and first part is assigned to the variable.
ppoliani
It is the logical OR operator and it simply says: If the left operand is a truthy value then return it otherwise return the right operand.
You could even, through the power of expressions, do this with a one-liner.
(MyArray[StringVariableName][StringVariableName2] || (MyArray[StringVariableName][StringVariableName2] = [])).push("whatever");
1 Comment
Sajith Mantharath
This is awesome. Is there any performance lag in this approach?
You could use the literal syntax to set things up like you'd have them:
var myObj = {
StringVariableName: {
StringVariableName2: []
}
};
myObj.StringVariableName.StringVariableName2.push("whatever");
1 Comment
Sachin Jain
You are doing it wrong way because StringVariableName looks like actually a variable name. You are making them as constant keys in the object.
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");
2 Comments
adrien
.push() is for arrays, not objects.
Sachin Jain
@A__ Both of us are correct as
myObject[str1][str2] is an array and not an object here.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.
MyArray = MyArray || [];