TS2339: Property 'includes' does not exist on type 'string'

Question

I have seen this error mentioned in regards to string arrays but not actual strings. I have a TypeScript file with the line

if (!bus.lineInfo.PublishedLineName.includes(input)) { 

This gives me an error of

TS2339: Property 'includes' does not exist on type 'string'. 

bus is a variable that implements the bus interface:

interface bus {     "lineInfo": {         "PublishedLineName": string,         "DestinationName": string, // The headsign of the bus         "Color": string,         "TextColor": boolean | string // false if this is "FFFFFF", otherwise it's the color     },     "warnings": boolean | busWarnings     "marker"?: google.maps.Marker,     "result"?: JQuery // The search result that appears in the sidebar } 

lineInfo.PublishedLineName is declared as a string, and String.prototype.includes() is a function according to MDN, so why does the TypeScript compiler complain about the missing property/method?

Answer 1

You should add es2016 or es7 lib complierOptions in tsconfig.json. Default TypeScript doesn't support some es6 polyfill functions

{   "compilerOptions": {     ...     "lib": [        "dom",        "es7"     ]   } } 

Or change build target to es2016 if you no longer want to support ES5 anymore

{   "compilerOptions": {     ...     "target" "es2016"   } } 

Answer 2

Add es2016.array.include to compilerOptions.lib