Operators and Decisions

An expression produces a value. Operators combine expressions. Arithmetic uses +, -, *, /, % (remainder), and ** (power). Comparisons use <, <=, >, >=, ===, and !==. Parentheses make precedence explicit.

const subtotal = 40;
const shipping = subtotal >= 50 ? 0 : 5;
console.log(subtotal + shipping); // 45

The conditional operator condition ? yes : no is useful for a short choice. Use if when branches do more work:

const score = 82;
if (score >= 90) {
  console.log("Excellent");
} else if (score >= 60) {
  console.log("Pass");
} else {
  console.log("Try again");
}

The conditions are tested from top to bottom. For score = 82, score >= 90 is false, then score >= 60 is true, so the program prints Pass and skips the remaining branch. If the order were reversed, a score of 95 would match the broad >= 60 case first and never reach Excellent. Order matters whenever ranges overlap.

&& and || short-circuit: the right side is evaluated only if needed. They return an operand, not necessarily a boolean. ?? uses the right side only when the left is null or undefined, which is useful when 0 and "" are valid values. Optional chaining, ?., stops property access when the value is nullish.

const settings = { retries: 0 };
console.log(settings.retries || 3); // 3 (often wrong)
console.log(settings.retries ?? 3); // 0
console.log(settings.user?.name ?? "Guest"); // Guest

For several fixed cases, switch is readable. Each case needs break unless falling through is intentional. Prefer if for ranges and complex conditions.

const command = "save";
switch (command) {
  case "save":
    console.log("Saving");
    break;
  case "delete":
    console.log("Deleting");
    break;
  default:
    console.log("Unknown command");
}

switch uses strict matching, so the string "1" does not match the number 1. Bitwise operators such as &, |, and << work on integer bit patterns and are useful for flags or binary protocols; they are different from logical && and ||. Do not use bitwise tricks as a replacement for clear arithmetic in ordinary application code.

Practice: Write shippingCost(total, isMember) that returns 0 for members or totals of at least 50, and 5 otherwise. Test the boundary at exactly 50.

Check: A solution can use if (isMember || total >= 50) return 0; return 5;. Test 49, 50, and a member with 0 to confirm both parts of the condition.

Operator precedence

Precedence determines which operation runs first. Multiplication runs before addition, and parentheses make a different grouping explicit:

console.log(2 + 3 * 4); // 14
console.log((2 + 3) * 4); // 20

When a condition has several && and || operators, add parentheses to show the intended groups even when you know the precedence rules. It helps the next reader and reduces mistakes when the condition changes. && and || short-circuit: they evaluate the right side only when needed, and return one of their operands rather than always returning a boolean.

const user = null;
const displayName = user && user.name; // null; does not read name
const label = user?.name ?? "Guest"; // "Guest"

Optional chaining (?.) stops a property access when its left side is null or undefined. Nullish coalescing (??) supplies a fallback only for those two values, while || also replaces valid values such as 0 and "". Choose based on which values your data considers absent.

Conditional expressions

Use if...else when branches contain several statements or when each branch deserves a clear block. The conditional operator (condition ? a : b) is an expression suited to a small choice that produces a value. Nested conditional operators are legal but quickly become hard to scan; prefer if or a lookup table for many cases.

switch compares its case values strictly and runs from the matching case until break, return, or the end. Add break unless fall-through is intentional and documented. For a finite set of keys, an object or Map of handlers can sometimes be easier to extend than a long switch.

Written By: Shiva Srivastava