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this and Binding

`this` is decided by how a function is called, except in arrow functions, which inherit it.

Key points

  1. 1

    Method call obj.fn() sets this to obj. A plain call fn() sets it to undefined in strict mode (modules and classes are always strict).

  2. 2

    call and apply invoke immediately with a chosen this; bind returns a new function with this fixed.

  3. 3

    Arrow functions have no this of their own; they use the surrounding scope's, so they suit callbacks inside methods.

  4. 4

    new Fn() creates a fresh object and binds this to it.

Common traps

  • Passing obj.method as a callback (to setTimeout or an event listener) loses this unless you bind it or wrap it in an arrow function.

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