Javascript
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Fundamentals
- 1 Fundamentals 11
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Hello World S
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Code structure S
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Use strict S
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Variables S
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Data types S
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Type conversions S
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Maths S
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Comparitions S
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Conditional S
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Loops S
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Functions S
- 2 Testing 2
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Mocha S
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Nested describe S
- 3 Objects 4
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Basics S
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Reference S
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Methods S
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Constructor S
- 4 Types 5
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Primitives S
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Numbers S
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Strings S
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Arrays S
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Json S
- 5 Classes 3
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Constructor S
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Binding S
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Inheritance S
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Javascript Fundamentals Variables
Variable declaration, let keyword Old var, visible through blocks var a = 1 // global let b = 2Variables
Let
To create a variable in JavaScript, use the let keyword.
/**
* To create a variable in JavaScript, use the let keyword
*/
let name;
let message = "Hello World";
console.log(name); // undefined
console.log(message); // Hello World
let a = 1, b = 2; // not recommended
Var
Variables, declared with var are visible through blocks.
/**
* In older scripts you find var keyword
* Var has no block scope, not used in modern scripts
*/
{
var a = 1; // global
let b = 2;
}
console.log(a); // 1
console.log(b); // ReferenceError: b is not defined
Const
To declare a constant, we use const instead of let.
/**
* To declare a constant, we use const instead of let
* Constants are named using capital letters and underscores
*/
const COLOR_BLUE = "#00F";
const COLOR_ORANGE = "#FF7F00";
let color = COLOR_ORANGE;
console.log(color); // #FF7F00
➥ Questions