JavaScript Sets
A JavaScript Set is a collection of unique values.
Each value can only occur once in a Set.
The values can be of any type, primitive values or objects.
How to Create a Set
You can create a JavaScript Set by:
- Passing an array to
new Set() - Create an empty set and use
add()to add values
The new Set() Method
Pass an array to the new Set() constructor:
Create a Set and add values:
Example
// Create a Set
const letters = new Set();
// Add Values to the Set
letters.add("a");
letters.add("b");
letters.add("c");
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Create a Set and add variables:
Example
// Create a Set
const letters = new Set();
// Create Variables
const a = "a";
const b = "b";
const c = "c";
// Add Variables to the Set
letters.add(a);
letters.add(b);
letters.add(c);
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The add() Method
If you add equal elements, only the first will be saved:
Example
letters.add("a");
letters.add("b");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
letters.add("c");
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Listing the Elements
You can list all Set elements (values) with a for..of loop:
Example
// Create a Set
const letters = new Set(["a","b","c"]);
// List all Elements
let text = "";
for (const x of letters) {
text += x;
}
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Sets are Objects
typeof returns object:
typeof letters; // Returns object
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instanceof Set returns true:
letters instanceof Set; // Returns true
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Browser Support
Set is an ES6 feature.
ES6 is fully supported in all modern browsers since June 2017:
| Chrome 51 |
Edge 15 |
Firefox 54 |
Safari 10 |
Opera 38 |
| May 2016 | Apr 2017 | Jun 2017 | Sep 2016 | Jun 2016 |
Exercise?What is this?
Test your skills by answering a few questions about the topics of this page
True or False.
Each value can only occur once in a Set.
