Javascript object props

Question

The syntax in JavaScript for accessing the property of an object is:

object.property or object["property"] or object[property]

I was trying out this lesson on freeCodeCamp:

var myObj = { gift: "pony", pet: "kitten", bed: "sleigh" };

function checkObj(checkProp) {
  if( myObj.hasOwnProperty(checkProp) )
    return myObj[checkProp];

  return "Not Found";
}

checkObj("gift");

... the console displays the expected prop with object[property] syntax and undefined otherwise. Why is this?

kind user · Answer 1 · 2018-12-14T16:54:31.713

3

Because only object[property] lets you to use a dynamic property (kept in a variable, in your particular case - checkProp).

The others - object.property or object["property"] refer directly to a prop named property, and since there isn't such prop as property, you'll receive undefined.

edited Dec 14 '18 at 16:54

answered Dec 14 '18 at 16:49

kind user

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Additional `object["proper ty"]` may contain spaces whereas `object.proper ty` may not – mplungjan Dec 14 '18 at 16:51

Giulio Bambini · Accepted Answer · 2018-12-14T16:58:41.813

1

Since property is a variable, to access the object property dynamically you must have to use Bracket ([]) notation. Otherwise it will always give you undefined.

var myObj = { gift: "pony", pet: "kitten", bed: "sleigh" };

function checkObj(checkProp) {
  if( myObj.hasOwnProperty(checkProp) )
    return myObj[checkProp];

  return "Not Found";
}

console.log(checkObj("gift"));
console.log(checkObj("g"));

edited Dec 14 '18 at 16:58

answered Dec 14 '18 at 16:53

Giulio Bambini

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Javascript object props

2 Answers2