JavaScript: Difference between revisions

JavaScript (view source)

447 bytes added , 22 January 2020

no edit summary

5,321

edits

@@ Line 3: / Line 3: @@
 ==Usage==
-===Arrays===
-<syntaxhighlight lang="javascript">
-let arr = [1,2,3];
-// Map
-arr.map(x => x > 2); // [false, false, true]
-// Reduce or Fold
-// Note that if you do not provide an initial accumulator,
-// then the first element will be your accumulator
-// I.e. the first call to your function will be (arr[0], arr[1])
-arr.reduce((acc, x) => acc + x, 0); // 6
-</syntaxhighlight>
 ===Canvas===
 ===Video===
@@ Line 88: / Line 74: @@
 </syntaxhighlight>
+==Data Structures==
+JavaScript traditionally has arrays and objects (hashmap) data structures.<br>
+ES2015 (ES6) adds several collections including: Map, Set, WeakMap, WeakSet
+===Arrays===
+<syntaxhighlight lang="javascript">
+let arr = [1,2,3];
+// Map
+arr.map(x => x > 2); // [false, false, true]
+// Reduce or Fold
+// Note that if you do not provide an initial accumulator,
+// then the first element will be your accumulator
+// I.e. the first call to your function will be (arr[0], arr[1])
+arr.reduce((acc, x) => acc + x, 0); // 6
+</syntaxhighlight>
+===Objects===
+Objects are maps in JavaScript. They are typically implemented as hashmaps by the JS engine.<br>
+Note that you can only use numbers and strings as keys.
+<syntaxhighlight lang="javascript">
+let my_map = {};
+my_map["my_key"] = "my_value";
+</syntaxhighlight>
 ==Modules==