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TypeError: "x" is read-only - JavaScript | MDN
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TypeError: "x" is read-only

    TypeError: "x" is read-only (Firefox)
    TypeError: 0 is read-only (Firefox)
    TypeError: Cannot assign to read only property 'x' of #<Object> (Chrome)
    TypeError: Cannot assign to read only property '0' of [object Array] (Chrome)

In this article

TypeError

?

.( .)

. .

, Object.defineProperty() Object.freeze() .

js
"use strict";
var obj = Object.freeze({ name: "Elsa", score: 157 });
obj.score = 0; // TypeError

("use strict");
Object.defineProperty(this, "LUNG_COUNT", { value: 2, writable: false });
LUNG_COUNT = 3; // TypeError

("use strict");
var frozenArray = Object.freeze([0, 1, 2]);
frozenArray[0]++; // TypeError

. .

js
"use strict";
Math.PI = 4; // TypeError

.

undefined , "undefined is not a function" :

js
"use strict";
undefined = function () {}; // TypeError: "undefined" is read-only

js
"use strict";
var obj = Object.freeze({ name: "Score", points: 157 });
obj = { name: obj.name, points: 0 }; // replacing it with a new object works

("use strict");
var LUNG_COUNT = 2; // a `var` works, because it's not read-only
LUNG_COUNT = 3; // ok (anatomically unlikely, though)

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  1. JavaScript
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    77. SyntaxError: raw bracket is not allowed in regular expression with unicode flag
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    95. TypeError: "x" is not a constructor
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    98. TypeError: "x" is read-only
    99. TypeError: already executing generator
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    107. TypeError: can't delete non-configurable array element
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    109. TypeError: can't set prototype of this object
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    1. JavaScript
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