11. Two phase interpretation, “hoisting” #

Created Tuesday 1 March 2022

• [ ] in vault

The two phases #

JavaScript is run in two phases by the JavaScript engine. The phases are:

1. Creation phase (or “hoisting”) - memory is reserved for variables and functions, i.e. they are declared but not defined.
2. Execution phase - here hoisted code is given value and all the code is executed.

Due to “hoisting”, this code does not raise an error:

console.log(a);
var a = 2;

Some caveats:

1. Function bodies are defined, in addition to being declared during “hoisting”, although variables are only declared not defined.
2. When using let, using code like the above (i.e. access before definition, due to the fact of “hoisting”) results in a ReferenceError.

What about nested code, how is that hoisted? #

Hoisting happens only for the current code level, not for nested code. See this. In short, hoisting is minimal (contained to the code level).

Sane practice #

One should avoid “using” hoisiting to access code at obscure places. It is nice to access code after it has been defined.