Handling null value in Javascript

Question

I have a Javascript function written as follows:

function refresh(selection, xPath, yPath, xAnnotationSelection, yAnnotationSelection) {
      var coords = selection.node().__coord__;
      ...
}

The function is being called sometimes, with the variable selection not having been set yet, which causes the following exception to be thrown:

Uncaught TypeError: Cannot read property 'coord' of null

What is a better way to write the statement so that it first checks to make sure that selection is not null, before attempting to call a method on it?

Pseudocode:

var coords = (selection ? ((selection.node ? selection.node().__coord__: null) : null);

Your pseudocode should work if you change selection.node to selection.node() — Barkha, Aug 25 '19 at 11:11
did you meaning you want at first check if the selection then do in it not found it should be default value null — Mohammed Al-Reai, Aug 25 '19 at 11:11
coords = selection ? (selection.node() ? selection.node().__coord__: null) : null; — Barkha, Aug 25 '19 at 11:13
Use a ternary operator only for simple to read expressions. For anything else go with regular `if` statements. The goal of good code is not to create fancy one-liners, but to create easily understandable and maintainable code. — t.niese, Aug 25 '19 at 11:18
or can be best coords = selection ? (selection.node() ? selection.node().__coord__: null) : null; or simple this code const section2= selection.node()?selection.node().__coord__: null; const coords=selection?section2:null or can used as if statment const icoords=null; if(selection&&selection.node()){ icoords=selection.node().__coord__ } — Mohammed Al-Reai, Aug 25 '19 at 11:23

score 0 · Answer 1 · answered Aug 25 '19 at 11:12

0

You can write -:

var coords = selection && selection.node && selection.node().__coord__;

answered Aug 25 '19 at 11:12

Abhisar Tripathi

1,569
10
21

Maxim Pyshko · Answer 2 · 2019-08-25T11:57:33.367

-1

I think the best way for your function is:

function refresh(selection, xPath, yPath, xAnnotationSelection, yAnnotationSelection) {
  const node = selection && selection.node();
  if (!node) {
    return null;
  }
  var coords = node.__coord__;
  ...
}

edited Aug 25 '19 at 11:57

answered Aug 25 '19 at 11:12

Maxim Pyshko

551
4
14

Handling null value in Javascript

2 Answers2