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, or when setting a private property that similarly only has a getter defined.

Message

TypeError: Cannot set property x of #<Object> which has only a getter (V8-based)
TypeError: '#x' was defined without a setter (V8-based)
TypeError: setting getter-only property "x" (Firefox)
TypeError: Attempted to assign to readonly property. (Safari)
TypeError: Trying to access an undefined private setter (Safari)

Error type

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 in strict mode. Classes are always in strict mode, so assigning to a getter-only private property always throws this error.

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 {{jsxref("Object.defineProperty()")}} page.

"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 the arc.temperature = 30 line, which attempts to set the temperature property, or you will need to implement a setter for it, for example like this:

"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

• {{jsxref("Object.defineProperty()")}}
• {{jsxref("Object.defineProperties()")}}