Summary - Debugging

JavaScript course · Beginner · Lesson 128/133

Test a calculation function using console.assert and console.trace.

Summary - Debugging

In this group you learned the core tools of debugging: the process (reproduce, isolate, understand, fix, verify), the call stack with console.trace, breakpoints with debugger, assertions with console.assert, and common bug patterns.

Now you will combine them: you will write a calculation function, check its expected result with console.assert and see the call trace with console.trace.

Exercise Assert the calculation function

Define a function called discount(price, rate). It should discount price by rate: return price - price * rate. Then check the expected result with console.assert(discount(100, 0.2) === 80, "discount wrong").

Show example solution

function discount(price, rate) {
  return price - price * rate;
}

console.assert(discount(100, 0.2) === 80, "discount wrong");

Exercise Write the full test

Define a function called half(n); it should return n / 2. Add the debugger statement inside the function. Then check the result with console.assert(half(10) === 5, "half wrong") and print the call trace with console.trace("half trace").

Show example solution

function half(n) {
  debugger;
  return n / 2;
}

console.assert(half(10) === 5, "half wrong");
console.trace("half trace");

Test yourself

Match the tool to its purpose

console.trace()

Shows the call stack
debugger

Pauses code and opens tools
console.assert(cond, msg)

Warns when condition is false
console.log(value)

Writes the value to console

Add the call trace

function run() {
  compute();
  console.____("run called");
}

Show answer

function run() {
  compute();
  console.trace("run called");
}

All lessons in Beginner

1 Variables and data types

Summary - Debugging