hoisting

As Stoyan Stefanov explains in “JavaScript Patterns” book, the hoisting is result of JavaScript interpreter implementation. The JS code interpretation performed in two passes. During the first pass, the interpreter processes variable and function declarations. The second pass is the actual code execution step. The interpreter processes function expressions and undeclared variables. Thus, we can … Read more

Functions are hoisted first, then variable declarations, per ECMAScript 5, section 10.5 which specifies how hoisting happens: We first have step 5 handling function declarations: For each FunctionDeclaration f in code, in source text order do… Then step 8 handles var declarations: For each VariableDeclaration and VariableDeclarationNoIn d in code, in source text order do… … Read more

Quoting MDN Docs on var hoisting, Because variable declarations (and declarations in general) are processed before any code is executed, declaring a variable anywhere in the code is equivalent to declaring it at the top. This also means that a variable can appear to be used before it’s declared. This behavior is called “hoisting”, as … Read more

The global a is set to 1 b() is called function a() {} is hoisted and creates a local variable a that masks the global a The local a is set to 10 (overwriting the function a) The global a (still 1) is alerted

In JavaScript variables are moved to the top of script and then run. So when you run it will do var myVar1; alert(myVar1); return false; This is because JavaScript doesn’t really have a true sense of lexical scoping. This is why it’s considered best practice to have all your variables declared at the top of … Read more