This is why the very general sounding name that is used. This is a pain.Ĭreating a variable to use by convention in both scopes is a solution for this very general problem with javascript (though it's useful in jquery functions, too). In the top level method this points to the object it is a method of (in this case, car) but in the inner function this now points to the global scope. This is specifically a problem when you create a function as a method of an object (like car.start in the example) then create a function inside that method (like activateStarter). you could also use car.starter, but using 'that' gives 'this.starter' is undefined, so we use 'that' instead. you can access car.starter inside this method with 'this' The this value is different in each context.I'm going to begin this answer with an illustration: var colours = ĭocument.getElementById('element').addEventListener('click', function() Static methods, static field initializers, and static initialization blocks belong to the static context. Constructors, methods, and instance field initializers ( public or private) belong to the instance context. This is the case for iterative array methods, the Promise() constructor, etc.Ī class can be split into two contexts: static and instance. Callbacks are typically called with a this value of undefined (calling it directly without attaching it to any object), which means if the function is non–strict, the value of this is the global object ( globalThis). When a function is passed as a callback, the value of this depends on how the callback is called, which is determined by the implementor of the API. When using these methods, the this substitution rules above still apply if the function is non-strict. Using (), you can create a new function with a specific value of this that doesn't change regardless of how the function is called. You can also explicitly set the value of this using the (), (), or Reflect.apply() methods. In typical function calls, this is implicitly passed like a parameter through the function's prefix (the part before the dot). Unicode character class escape: \p // Only for demonstration - you should not mutate built-in prototypes Number.Character class escape: \d, \D, \w, \W, \s, \S.Enumerability and ownership of properties.
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