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Scope and Variable Lifetime

8 exercisesIntermediate

Scope determines where a variable can be read. Variables declared inside a function stay local to that call, while let and const inside a block are unavailable once the block ends.

const unit = "points";

function formatScore(score) {
  const label = `${score} ${unit}`;
  return label;
}

console.log(formatScore(9)); // 9 points
// console.log(label);       // ReferenceError

Small tracing exercises reveal function and block scope, accidental shadowing, and out-of-scope access. Keeping values in the smallest useful scope reduces surprising interactions elsewhere in a program.

Read a Global ValueStart Keep a Function LocalStart Use a Block-Scoped ValueStart Repair an Out-of-Scope TotalStart Avoid Shadowing a ScoreStart Trace a Loop CounterStart Reset a Local on Each CallStart Scope-Safe ScoreboardStart