Flash cards
Review the key moves
1/4
Core idea
What is the main idea behind TypeScript Arrays?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
1Quick choice
Which statement best captures the main point of this lesson?
2Fill blank
Complete the missing token from the example code.
___ names: string[] = [];3Order
Put the learning moves in the order that makes the concept easiest to apply.
The readonly keyword can prevent arrays from being changed.
Read more about arrays in our JavaScript Array chapter .
TypeScript has a specific syntax for typing arrays.
TypeScript has a specific syntax for typing arrays.
Read more about arrays in our JavaScript Array chapter .
Example
const names: string[] = [];
names.push("Dylan"); // no error
// names.push(3); // Error: Argument of type 'number' is not assignable to parameter of type 'string'.Readonly
The readonly keyword can prevent arrays from being changed.
Example
const names: readonly string[] = ["Dylan"];
names.push("Jack"); // Error: Property 'push' does not exist on type 'readonly string[]'.
// try removing the readonly modifier and see if it works?Type Inference
TypeScript can infer the type of an array if it has values.
Example
const numbers = [1, 2, 3]; // inferred to type number[]
numbers.push(4); // no error
// comment line below out to see the successful assignment numbers.push("2"); // Error: Argument of type 'string' is not assignable to parameter of type 'number'.
let head: number = numbers[0]; // no error