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JavaScript - what is scope?

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Created by:

cory

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Scope determines the accessibility of variables. In JavaScript there are available few scopes.

1. global scopes (when variables are places direcly inside script)

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var a = 123;
var b = true;
​
console.log(a);  // 123
console.log(b);  // true

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Note: there is alternative way to create and access global variables:
- NodeJS JavaScript:
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global.c = 'global variable';
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console.log(c);
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console.log(global.c);
- WebBrowser JavaScript:
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<html>
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<body>
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<script>
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    window.c = 'global variable';
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    console.log(c);
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    console.log(window.c);
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</script>
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</body>
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</html>
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2. Local scopes: Function scopes

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var a = 123;
​
function logNumber() {
    var a = 'text';
​
    console.log(a);
}
​
logNumber();  // text
console.log(a);  // 123

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3. Local scopes: curly braces scopes

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That scope works with let and const variables (it was introduced in ECMAScript 6 (ES6/ES2015)).

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let a = 1;
​
{ // this brackets create new scope for let keyword variables
    let a = 2;
​
    console.log(a); // 2
}
​
console.log(a); // 1