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Debugging Your Javascript Code

Web browsers generally have consoles, which are interactive command lines where you can print text and test pieces of code.

This is where, for the most part, you’ll be debugging your javascript code and checking out for errors.

How To Open The Console

To open up the console for any browser.

  1. right-click on your webpage and choose “inspect” or “inspect element” if you’re on Safari browser.
A Google Chrome illustration
A Safari illustration

2. Next, select console

A Google Chrome console illustration

Printing Values Using console.log()

console.log("This is the browser console");

//This is a browser console

Printing Multiple Values

console.log('abc', 123, true);
//abc 123 true

Printing Strings With Substitutions

Here are some directives you can use for your substitutions:

%s: converts the corresponding value to a string and inserts it

console.log('Value: %s %s', 123, 'abc');

//123 abc

%o: inserts a string representation of an object

console.log('%o', {foo: 123, bar: 'abc'});
A snapshot of the result of the above program

Notice that result is an object.

%j: converts a value to a JSON string and inserts it

console.log('%j', {foo: 123, bar: 'abc'});
A snapshot of the result of the above program

%%: inserts a single %

console.log('%s%%', 100);

// 100%

Printing Error Information Using console.error()

console.error() works typically the same way as console.log(), but what it logs is considered error information.

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