JavaScript | Symbol.unscopables Properties
The Symbol.unscopables property in Javascript is a well-known symbol that is used to specify an object value of whose own and inherited property names are excluded from the environment bindings.
Syntax:
object[Symbol.unscopables]
Property attributes: This property holds an Object and it is not Writable, Enumerable and Configurable.
Return value: Check the variable appear in lexical scope variable.
Below examples illustrate the Symbol.unscopables properties in JavaScript:
Example 1: If all property are set to false.
// JavaScript to illustrate Symbol.toPrimitive var obj1 = { val: "Have", val1: "FUN"}; obj1[Symbol.unscopables] = { val1: false, val: false }; with (obj1) { console.log(val1); } with (obj1) { console.log(val); } |
Output:
> "FUN" > "Have"
Example 2: If any property are set to true.
// JavaScript to illustrate Symbol.toPrimitive var obj1 = { val: "Have", val1: "FUN"}; obj1[Symbol.unscopables] = { val1: false, val: true }; with (obj1) { console.log(val1); } with (obj1) { console.log(val); } |
Output:
"FUN" Error: val is not defined
Example 3:
var list = []; with (Array.prototype) { list.push('unscopables');} console.log(Object.keys(Array.prototype[Symbol.unscopables])); |
Output:
[ 'copyWithin', 'entries', 'fill', 'find', 'findIndex', 'flat', 'flatMap', 'includes', 'keys', 'values' ]
Supported Browsers: The browsers supported by JavaScript Symbol.unscopables properties are listed below:
- Google Chrome 45
- Edge 12 and above
- Firefox 48 and above
- Opera 32 and above
- Safari 9 and above
Reference: https://devdocs.io/javascript/global_objects/symbol/unscopables
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