Mutability

Mutability && Primitive && Reference Examples
Objects are passed by reference, are mutable, and can be modified by our functions:
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function rotateLeft(arr, num) {
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    for (let i = 0 ; i < num; i++) {
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        let el = arr.pop();
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        arr.unshift(el);
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    }
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}
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let myArr = [1, 2, 3, 4, 5,];
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rotateLeft(myArr, 2);
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console.log(myArr);
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Strings are passed by value, are immutable, and a new array is constructedd and returned, because it cannot be changed in place.
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function rotateString(str, num) {
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    return str.slice(num) + str.slice(0, num);
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}
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​
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let str = "foobar";
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let ret = rotateString(str, 3);
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console.log(str);
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console.log(ret);
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Dereferencing
Arrays
To dereference an array, use let [var1, var2] syntax.
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let arr = ['one', 'two', 'three'];
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​
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let [first] = arr;
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console.log(first);
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Objects
To dereference attributes from an object, use let {} syntax.
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let me = {
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    name: "Ian",
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    instruments: ['bass', 'synth', 'guitar'],
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    siblings: {
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        brothers: ['Alistair'],
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        sisters: ['Meghan']
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    }
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}
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​
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let { name, instruments: musical_instruments, siblings: {sisters}} = me;
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​
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console.log(sisters);
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function printInstruments({ instruments } ) {
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    console.log(instruments);
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}
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printInstruments(me);
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​
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function printSiblings({ siblings: {sisters, brothers}}) {
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    console.log("Sisters", sisters);
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    console.log("Brothers", brothers);
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}
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​
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printSiblings(me);
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​
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​
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​
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//rest parameters
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// combines parameters into array
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​
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...parameterName
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​
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splice is an example of where we've seen this before
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​
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let arr = 'my dog has fleas'.split(' ');
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arr.splice(3, 1, 'trees')
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​
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​
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//spread operator
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// take an arrray and spread them into arguments
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​
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...argContainer
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​
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OR
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​
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// take an object or array and spread their elements/attributes into another object or array
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​
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​
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​
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function multiply(multiplier, ...theArgs) {
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  return theArgs.map(function(element) {
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    return multiplier * element
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  })
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}
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​
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let arr = multiply(2, 1, 2, 3)
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console.log(arr)
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​
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​
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​
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​
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let me = {
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    name: "Ian",
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    instruments: ['bass', 'synth', 'guitar'],
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    siblings: {
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        brothers: ['Alistair'],
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        sisters: ['Meghan']
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    }
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}
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​
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let countryArr = ['USA', 'Canada', 'UK'];
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//me[countries] = countryArr;
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​
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let myCountries = {
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  'countries': countryArr
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};
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​
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let newMe = {...me, ...countries}
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Scope

Array-CB-Methods

Last modified 2mo ago

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Contents

Mutability && Primitive && Reference Examples

Dereferencing

Arrays

Objects