Type coercion and equality operators

What the exam expects

• Predict the result of +, -, * and += when one operand is a string, null, undefined, an array or an object.
• Evaluate ==, === and Object.is() for mixed types, null/undefined, NaN and -0, and know that switch uses strict equality.
• Predict < and > when both operands are strings versus when one is a number.
• Convert explicitly with Number(), unary +, String() and Boolean(), and test for NaN with Number.isNaN().
• Know the typeof results that surprise people: null, NaN, arrays and functions.
• Key terms: coercion (an implicit, automatic type conversion); explicit conversion (calling Number(), String() or Boolean() yourself); primitive coercion (turning an object into a primitive by valueOf() or toString()); loose equality (==, converts types first); strict equality (===, never converts).

Key facts

Check yourself