Replacing value in an Array in typescript

Question

I have an Array localData defined as:

public localData: Array<any> = [];

In the sample below it has length of 2 and following values in developer tools.

(2) [{…}, {…}]
0:
Country: "United States"
DataSource: ""
FunctionName: "Customer Service"
GroupName: "Main"
Index: 0
Result: undefined
StartDate: "5/1/2012"
StopDate: "
"
1:
Country: "United States"
DataSource: ""
FunctionName: "Customer Service"
GroupName: "Main"
Index: 1
Result: undefined
StartDate: ""
StopDate: "5/1/2019
"
__proto__: Object
length: 2
__proto__: Array(0)  

I need to replace the DataSource value to, if blank or if it has any other value then, to a certain value. I tried doing:

 this.localData.forEach(x => x.DataSource ? '' || 'XXX' : 'MyVAL');

This code doesn't throw any error but DataSource still remains blank. Has anyone had this issue before, or knows why this is happening?

Answer 1

You're not using assignment. As Doc explains, forEach run the provided function for each element, and your function simply return a boolean if x.DataSource exist, a string otherwise.

If your goal is to change your array you can either modify your function with an assignment:

this.localData.forEach(x =>  {
   x.DataSource = x.DataSource ? '' || 'XXX' : 'MyVAL'
});

or simply use the map function

this.localData = this.localData.map( item => {
   item.DataSource = item.DataSource ? '' || 'XXX' : 'MyVAL'
   return item;
});

Clarification: in your code line

this.localData.forEach(x => x.DataSource ? '' || 'XXX' : 'MyVAL');

the ternary operator is gonna return 'MyVAL' if x.DataSource is undefined or the empty string, and always 'XXX' if all the other cases. If i get it right, you want to do something like:

x.DataSource && x.DataSource !== 'XXX' ? 'MyVAL' : x.DataSource;

which can be read as: if DataSource is evaluated and it's different from 'XXX' assign 'MyVal', keep it as it is otherwise.

EDIT: clarification

Answer 2

try following way:

this.localData.forEach(x => (!x.DataSource || x.DataSource === 'XXX') ? 'MyVAL' : x.DataSource);

Where

!x.DataSource means x.DataSource === ''