The displayName property is not initially present on any function — it's added by the code authors. For the purpose of display, it should be a string.

The displayName property, if present, may be preferred by consoles and profilers over the name property to be displayed as the name of a function.

Among browsers, only the Firefox console utilizes this property. React devtools also use the displayName property when displaying the component tree.

Firefox does some basic attempts to decode the displayName that's possibly generated by the anonymous JavaScript functions naming convention algorithm. The following patterns are detected:

• If displayName ends with a sequence of alphanumeric characters, _, and $, the longest such suffix is displayed.
• If displayName ends with a sequence of []-enclosed characters, that sequence is displayed without the square brackets.
• If displayName ends with a sequence of alphanumeric characters and _ followed by some /, ., or <, the sequence is returned without the trailing /, ., or < characters.
• If displayName ends with a sequence of alphanumeric characters and _ followed by (^), the sequence is displayed without the (^).

If none of the above patterns match, the entire displayName is displayed.

By entering the following in a Firefox console, it should display as something like function MyFunction():

const a = function () {};
a.displayName = "MyFunction";

a; // function MyFunction()

You can dynamically change the displayName of a function:

const object = {
  // anonymous
  someMethod: function someMethod(value) {
    someMethod.displayName = `someMethod (${value})`;
  },
};

console.log(object.someMethod.displayName); // undefined

object.someMethod("123");
console.log(object.someMethod.displayName); // "someMethod (123)"

Firefox devtools would clean up a few common patterns in the displayName property before displaying it.

function foo() {}

function testName(name) {
  foo.displayName = name;
  console.log(foo);
}

testName("$foo$"); // function $foo$()
testName("foo bar"); // function bar()
testName("Foo.prototype.add"); // function add()
testName("foo ."); // function foo .()
testName("foo <"); // function foo <()
testName("foo?"); // function foo?()
testName("foo()"); // function foo()()

testName("[...]"); // function ...()
testName("foo<"); // function foo()
testName("foo..."); // function foo()
testName("foo(^)"); // function foo()

Not part of any standard.

• Function.prototype.name