Property 'trimLeft' does not exist on type 'string'. Lib: ["dom", "es2018"]
Include the library "es2019.string"
. Update your copy of Typescript if there is no such library. It is rather new and did not exist when this question was asked.
Update the typescript library to "typescript": "~3.6.2". Include "es2019" in the tsconfig.json lib's array. It will work.
"target": "es2015",
"typeRoots": [
"node_modules/@types"
],
"lib": [
"es2018",
"es2019",
"dom"
]