strange behavior when using Underscore when testing equals condition

Question

I am using Underscore.js in my project and came across a weird behavior. When I filter the array with changes_summary === 2 I am getting the desired result but when I use the same with changes_summay === 0, I am not getting any output.

Following is the code:

var result={
   "data": [
     {
      "id": 956,
      "changes_summary": 2,
      "name": "Pradeep",
      "age": 32
     },
     {
      "id": 956,
      "changes_summary": 0,
      "name": "praveen",
      "age": 22
     }
  ]
}


var filtered = _.filter(result.data, function(obj){ 
    return (obj.changes_summary && obj.changes_summary === 2)
});
//working when comparing with changes_summary with 2 but not working when comparing with 0
console.log(filtered);

Please let me know where I am going wrong. Link to Jsfiddle attached: Jsfiddle

obj.changes_summary && remove this to check for 0. 0 is falsy See jsfiddle.net/tusharj/2j13o0be/1 — Tushar
– Tushar, Commented Jul 22, 2015 at 13:30
@Tushar removing it is not necessarily the right thing. If the filter is only supposed to apply to objects that definitely have the property, then an additional test is necessary. — Pointy
– Pointy, Commented Jul 22, 2015 at 13:31

Pointy · Accepted Answer · 2015-07-22 13:28:54Z

1

The first test — obj.changes_summary — will fail when the property value is 0 because that's a falsy value. If you're testing to see if the property is present in the object, you can do this:

return (("changes_summary" in obj) && obj.changes_summary === 0);

answered Jul 22, 2015 at 13:28

Pointy

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2 Comments

mu is too short Over a year ago

Is the in even needed?

Pointy Over a year ago

@muistooshort well it depends on the intention - if the idea is to filter out objects that definitely have the property and for which the property value is 0, then it's necessary. If objects without the property should be treated as if the property value is 0, then no.

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