CODEWITHSUNDEEP
javascriptif-statementternary-operator
pourrait Peut-être
pourrait Peut-être

Reputation: 291

JavaScript: When the `condition` portion of a `ternary` or `if` statement does not include `===` or `>=`

In the condition portion of the following ternary statement, does playlist.length equal playlist.length >= 1 ?

var playlist = ["video1", "video2", "video3", "video4", "video5"];

// some code here

alert ((playlist.length) ?
     playlist.length + "video(s) remain in the playlist: " + playlist.join (", ") + "." 
    : "No videos remain in the playlist");

Likewise, in the following snippet of code, does ! playlist.length equal playlist.length === 0 ?

alert ((! playlist.length) ?
     "No videos in the playlist."
    : playlist.length + " video(s) remain in the playlist: " + playlist.join(", ") + ".");

This is the first time I've seen an example where the condition portion of a ternary or if statement does not include such a notation as === or >=. So I'm not sure how to interpret this.

Upvotes: 3

Views: 2348

Answers (4)

JCOC611
JCOC611

Reputation: 19719

The two are very similar: !playlist.length and playlist.length === 0.

However, they are not exacty the same. In fact, here:

var playlist1 = [];
var playlist2 = {};
!playlist1.length // true
!playlist2.length // true
playlist1.length === 0 // true
playlist1.length === 0 // false

In that sense !playlist.length also can be used on all kinds of objects, not just arrays.

In any case, when using this on an array, it is a way to check if the array is empty, and works as you have suggested, the same as playlist.length === 0.

Upvotes: 1

Jairo
Jairo

Reputation: 350

In javascript 0 equals false, and any other number value equals true, but if you use === it compare value types too.

Upvotes: 0

Travis J
Travis J

Reputation: 82277

0 is implicitly converted to false in boolean comparisons in JavaScript. So when the length is 0, that is false. Conversely, any other number is implicitly converted to true in boolean comparisons in JavaScript. So when the length is anything but 0 it is true.

An easy test is to use !! to see the "truthy" value

!!1 === true
!!0 === false
!!6 === true

Upvotes: 4

PaulProgrammer
PaulProgrammer

Reputation: 17630

The part to the left of the ? is simply evaluated for "truthiness". The value 0 is "falsy" so evaluates as false for the purposes of the test. Numeric values other than 0 are "truish" and therefore for this purpose evaluate to true.

All other behaviors of the ternary are the same.

The === and !== simply add the additional constraint that the L-value and R-value must also be the same type.

Upvotes: 1

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