![]() The following will throw a ReferenceError because the names x, y, and z have no meaning outside of the function f.Ĭonsole.log(typeof foo) // undefined, because `foo` is block-scoped In eval strings, variables declared using var will be placed in the current scope, or, if eval is used indirectly, as properties on the global object. In non-strict mode, implicitly defined properties on the global object have global scope, because the global object sits at the top of the scope chain. Implicitly defined properties on the global object Named function expressions are scoped to themselves (e.g., for the purpose of recursion). Note: non-strict mode is a complicated set of emergent rules based on the quirky historical implementations of different browsers. Function declarationsįunction declarations have block scope in strict mode and function scope in non-strict mode. ![]() Functions declared as default arguments close over the parameter list, and not the body of the function. Note that there is a slight complexity to this. The interim period is known as the temporal dead zone.į() // 1 because x is hoisted even though declared with `let`!įunction parameter names are scoped to the function body. However, variables declared using let and const cannot be read or assigned to until control has passed the point of declaration in the source code. This means that their logical position of definition is the top of their enclosing scope (block or function). Note: let, const and var are all hoisted. Identifiers declared using let and const have block scope, apart from when they are declared directly in the global context, in which case they have global scope. There are separate rules for their use in eval functions. Identifiers declared using var have function scope, apart from when they are declared directly in the global context, in which case they are added as properties on the global object and have global scope.
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