JavaScript syntax
part 12/59 · 107.4 KB total
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
z = 'penguins'; // Closure: Child function is able to access the variables of the parent function.
}
twenty = 20; // This variable is declared on the next line, but usable anywhere in the function, even before, as here
var twenty;
child();
return x1 + x2; // We can use x1 and x2 here, because they are global
}
f();
console.log(z); // This line will raise a ReferenceError exception, because the value of z is no longer available
for (let i = 0; i < 10; i++) console.log(i);
console.log(i); // throws a ReferenceError: i is not defined
for (const i = 0; i < 10; i++) console.log(i); // throws a TypeError: Assignment to constant variable
for (const i of [1,2,3]) console.log(i); //will not raise an exception. i is not reassigned but recreated in every iteration
const pi; // throws a SyntaxError: Missing initializer in const declaration
Primitive data types
The JavaScript language provides six primitive data types:
• Undefined
• Number
• BigInt
• String
• Boolean
• Symbol
Some of the primitive data types also provide a set of named values that represent the extents of the type boundaries. These named values are described within the appropriate sections below.
Undefined
The value of "undefined" is assigned to all uninitialized variables, and is also returned when checking for object properties that do not exist. In a Boolean context, the undefined value is considered a false value.
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────