Determine if external javascripts are loaded correctly

Question

I have some external thirdparty js files on my page, let say:

3rdparty1.js

And also I have one of my own:

myown1.js

I want to perform a condition in myown.js that asks if 3rdparty1.js is successfully loaded or not (e.g. No internet connection, error 404, suddenly third party makes 3rdparty1 private, etc.) similar to this code:

// inside myown1.js
if(3rdparty1.js_is_loaded_correctly) {

    // performs function found inside 3rdparty1.js
    3rdparty1function();
} else {

    // performs an alternative function (maybe found inside myown.js)
    myownjsbackupfunction();

    // or maybe show prompt messages
    alert("Some functionalities are not available at the moment."
        + " Try reloading this page later.");
}

Now, how do you write the proper condition statement for this? Note that 3rdparty1.js is on a separate domain, if that helps.

Thanks!

You could check if some symbols exported from that library exist. if (window.something3rdpartyprovided) { ... } . — Thilo
– Thilo, Commented May 7, 2015 at 7:06

Denys Séguret · Accepted Answer · 2015-05-07 07:06:12Z

3

Check whether 3rdparty1function has been declared:

if (typeof 3rdparty1function !== "undefined") {
    // library OK

answered May 7, 2015 at 7:06

Denys Séguret

384k90 gold badges813 silver badges780 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Gideon Over a year ago

Thanks! Your a lifesaver.

Gideon Over a year ago

A... wait, is (typeof 3rdparty1function === "function") valid also?

Denys Séguret Over a year ago

@Gideon Yes but the common practice is to test for the definition of the variable. It's best to use it so that other developers recognize your intent.

Collectives™ on Stack Overflow

Determine if external javascripts are loaded correctly

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related