JavaScript (JS) Cheat Sheet

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How to include an external JavaScript file?

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<script src="filename.js"></script>

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What is the syntax for a function in JavaScript?

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function addNumbers(a, b) { return a + b; }

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How do you edit a DOM element in JavaScript?

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document.getElementById("elementID").innerHTML = "Hello World!";

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How to output data to the browser console in JavaScript?

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console.log(a);

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What is the syntax for a for loop in JavaScript?

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for (var i = 0; i < 10; i++) { document.write(i + ": " + i*3 + "
"); }

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How do you declare a variable in JavaScript?

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var a; // variable a = 1; // assignment

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What is the purpose of 'use strict' in JavaScript?

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"use strict"; // Use strict mode to write secure code

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How do you create an array in JavaScript?

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var dogs = ["Bulldog", "Beagle", "Labrador"]; // array

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What is the syntax for an if-else statement in JavaScript?

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if ((age >= 14) && (age < 19)) { status = "Eligible."; } else { status = "Not eligible."; }

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How do you handle errors in JavaScript?

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try { // code to try } catch(err) { console.log(err.message); }