My JavaScript function does one thing when it gets the wrong input

Question

I have a function that's meant to get media playing status from a GET request and do something accordingly depending on whether the media returns playing or not.

My function:

function get_media() {
    fetch('http://127.0.0.1:5000/get_media')
    .then(function(resp) { return resp.json() }) // Convert data to json
    .then(function(data) {
        var songTitle = data.title
        var artist = data.artist
        var playingStatus = data.playing
        console.log(playingStatus)
        if (playingStatus = "true") {
            console.log("playing")
            document.getElementById("play").style.display = "none";
            document.getElementById("pause").style.display = "block";
            document.getElementById('song-title').innerHTML = songTitle;
            document.getElementById('artist-name').innerHTML = artist;
        } 
        if (playingStatus = "false") {
            console.log("paused")
            document.getElementById("play").style.display = "block";
            document.getElementById("pause").style.display = "none";
            document.getElementById('song-title').innerHTML = songTitle;
            document.getElementById('artist-name').innerHTML = artist;
        }
    })
}

The issue is, even if playingStatus is set to false, the function still does the action specified in if (playingStatus = "true"), as shown in this screenshot below of the console.

The console tells me playingStatus is set to false, but is activating the wrong condition in the if statement. Why is this happening?

By doing playingStatus = "false", you're assigning the string "false" to playingStatus. To test for equality, use == — Jonathan Hamel
– Jonathan Hamel, Commented Apr 10, 2021 at 16:33

ray · Accepted Answer · 2021-04-10 16:44:52Z

3

Short answer:

By doing playingStatus = "true" you're assigning a value to playingStatus, not comparing it against the value. If you want to test whether it's a particular value you should use === or ==, as in playingStatus === "true".

Why `if (playingStatus = "true")` is always true:

Because an assignment expression evaluates to the assigned value, the expression playingStatus = "true" will evaluate to "true", and because "true" is truthy, the condition if (playingStatus = "true") will always be true.

String vs boolean:

Another possible issue is that true and false may not be strings, so you might need to lose the quotes, e.g. playingStatus === true.

edited Apr 10, 2021 at 16:44

answered Apr 10, 2021 at 16:35

ray

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Comments

WoaItsBren · Accepted Answer · 2021-04-10 16:33:38Z

0

Right, sorry, it turns out I was using = instead of == in my if statement. It should've been if (playingStatus == "false") not if (playingStatus = "false").

Still curious why the first statement returned true, though.

answered Apr 10, 2021 at 16:33

WoaItsBren

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1 Comment

Jonathan Hamel Over a year ago

The assignment of "true" to playingStatus is truthy

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My JavaScript function does one thing when it gets the wrong input

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Why `if (playingStatus = "true")` is always true:

String vs boolean:

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Short answer:

Why if (playingStatus = "true") is always true:

String vs boolean:

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