JavaScript Variables Lifecycles

Understand const in JavaScript: when to use it, how it differs from let and var, and how mutations behave with arrays and objects versus primitive types, plus scope and hoisting.

Explore when to use const, let, and var in JavaScript by examining scope, temporal variables, and hoisting, and learn how declaration choice signals intent to other developers.

Practice using let, var, and const correctly while refactoring code that computes odd and even numbers, returning an object with odd numbers and even counts, following guidelines.

The lecture emphasizes declaring variables before first usage, using strict mode, and managing scope with let and const to avoid global leakage and explain hoisting.

Explore vanilla JavaScript interactivity by toggling the active class on menu items using let and var, with event handlers, querySelectorAll, and for loops, and compare let versus var behavior.

Discover how the JavaScript engine compiles code, then executes it, tracks variable declarations across global and function scopes with an activation object, and explains three phases of the variable lifecycle.

Explore how undeclared variables behave in JavaScript, including global scope leakage in non-strict mode, reference errors, and why always declaring variables matters.

Examine the let lifecycle: declaration in compilation, initialization in execution, and the temporal dead zone that blocks access before declaration. Understand reference errors before initialization and value changes after assignment.

Explore how the JavaScript engine transitions from compilation to execution, resolving declarations in global, function, and block scopes, initializing variables, evaluating conditions, and executing a function with arguments.