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content/20201009090331-javascript_array_methods.md

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+---
+id: c76b3766-a1ed-43f9-bdb6-4076e6bb5b7a
+title: JavaScript Array Methods
+---
+
+# ES6
+
+## Static Array methods
+
+### Array.from()
+
+``` javascript
+const arr2 = Array.from(arguments); // ES6
+```
+
+If a value is [iterable](20201014092625-javascript_iterables) (as all
+Array-like DOM data structure are by now), you can also use the
+[spread](20201014094144-spread) operator (…) to convert it to an
+[Array](20200826201029-arrays):
+
+``` javascript
+const arr1 = [...'abc'];
+    // ['a', 'b', 'c']
+const arr2 = [...new Set().add('a').add('b')];
+    // ['a', 'b']
+```
+
+### Array.of()
+
+This returns an array of the passed parameters
+
+``` javascript
+console.log(Array.of(1, 2, 3, 4)) // [1, 2, 3, 4]
+```
+
+## Array.prototype methods
+
+### Array.prototype.fill()
+
+``` javascript
+const arr2 = new Array(2).fill(undefined);
+    // [undefined, undefined]
+```
+
+### Array.prototype.copyWithin()
+
+The method signature is:
+
+``` typescript
+Array.prototype.copyWithin(target : number,
+    start : number, end = this.length) : This
+```
+
+It copies the elements whose indices are in the range \[start,end) to
+index target and subsequent indices. If the two index ranges overlap,
+care is taken that all source elements are copied before they are
+overwritten. I am confused as to how this is in any way useful.
+
+``` javascript
+const arr = [0,1,2,3];
+console.log(arr.copyWithin(2, 0, 2)) // [0, 1, 0, 1]
+```
+
+### Searching for elements
+
+1.  Array.prototype.findIndex()
+
+    ``` javascript
+    console.log([6, -6, 8].findIndex(x => x < 0)) // 1
+    ```
+
+2.  Array.prototype.find()
+
+    ``` javascript
+    console.log([6, -6, 8].find(x => x < 0)) // -6
+    ```
+
+### Iteration
+
+1.  Array.prototype.entries()
+
+    ``` javascript
+    console.log(Array.from(['a', 'b'].entries())) // [ [ 0, 'a' ], [ 1, 'b' ] ]
+    ```
+
+2.  Array.prototype.values()
+
+    ``` javascript
+    console.log(Array.from(['a', 'b'].values())) // ['a', 'b']
+    ```
+
+3.  Array.prototype.keys()
+
+    ``` javascript
+    console.log(Array.from(['a', 'b'].keys())) // [0, 1]
+    ```
+
+# ES2016
+
+## Array.prototype.includes()
+
+Tells you if array includes a certain element:
+
+``` javascript
+console.log(["a", "b", "c"].includes("a")); // true
+console.log(["a", "b", "c"].includes("d")); // false
+```