How can I define a Typescript object return value for a function?

Question

My function looks like this:

parseRange = (text) => {     var arr = [];     var lower = null;     var upper = null;     if (!text || text === "") {         lower = null;         upper = null;     }     else if (text.indexOf("-") > 0) {         arr = text.split("-");         lower = +arr[0];         upper = +arr[1];     }     else {         lower = +text;         upper = null;     }     return {         lower: lower,         upper: upper     }; }; 

I am familiar with returning strings and numbers but how can I specify the return is an object with a lower and upper parameter?

Answer 1

parseRange = (text: string) : { lower: number; upper: number; } => {     // ...     return {         lower: lower,         upper: upper     }; }; 

or

parseRange = <(text: string) : { lower: number; upper: number; }> ((text) => {     // ...     return {         lower: lower,         upper: upper     }; }); 

or

var parseRange : (text: string) => { lower: number; upper: number; } = (text) => {     // ...     return {         lower: lower,         upper: upper     }; }; 

or

parseRange = function (text: string) : { lower: number; upper: number; } {     // ...     return {         lower: lower,         upper: upper     }; }; 

or

function parseRange(text: string) : { lower: number; upper: number; } {     // ...     return {         lower: lower,         upper: upper     }; }; 

or

interface RangeResult {     lower: number;     upper: number; } function parseRange(text: string) : RangeResult {     // ...     return {         lower: lower,         upper: upper     }; }; 

Answer 2

TypeScript infers function return types, so this results in a compile error without having to specify the types explicitly:

var parseRange = (text) => {     return {         lower: 5,         upper: 6     }; };  var range = parseRange(""); range.foo; // compile error 

Live example which shows the error:

The property 'foo' does not exist on value of type '{ lower: number; upper: number; }'.