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TypeError: setting getter-only property "x"

The JavaScript strict mode-only exception "setting getter-only property" occurs when there is an attempt to set a new value to a property for which only a getter is specified.

Message

TypeError: Cannot set property x of #<Object> which has only a getter (V8-based)
TypeError: setting getter-only property "x" (Firefox)
TypeError: Attempted to assign to readonly property. (Safari)

Error type

TypeError in strict mode only.

What went wrong?

There is an attempt to set a new value to a property for which only a getter is specified. While this will be silently ignored in non-strict mode, it will throw a TypeError in strict mode.

Examples

Property with no setter

The example below shows how to set a getter for a property. It doesn't specify a setter, so a TypeError will be thrown upon trying to set the temperature property to 30. For more details see also the Object.defineProperty() page.

js
"use strict";

function Archiver() {
  const temperature = null;
  Object.defineProperty(this, "temperature", {
    get() {
      console.log("get!");
      return temperature;
    },
  });
}

const arc = new Archiver();
arc.temperature; // 'get!'

arc.temperature = 30;
// TypeError: setting getter-only property "temperature"

To fix this error, you will either need to remove line 16, where there is an attempt to set the temperature property, or you will need to implement a setter for it, for example like this:

js
"use strict";

function Archiver() {
  let temperature = null;
  const archive = [];

  Object.defineProperty(this, "temperature", {
    get() {
      console.log("get!");
      return temperature;
    },
    set(value) {
      temperature = value;
      archive.push({ val: temperature });
    },
  });

  this.getArchive = function () {
    return archive;
  };
}

const arc = new Archiver();
arc.temperature; // 'get!'
arc.temperature = 11;
arc.temperature = 13;
arc.getArchive(); // [{ val: 11 }, { val: 13 }]

See also

© 2005–2023 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Getter_only