TypeScript's Conversion of Code to JavaScript: A Comprehensive Guide to the 'Target' Option
When the Target is set to es5, TypeScript simulates classes using JavaScript functions because es5 does not support classes. When set to es2015 (es6), TypeScript can generate code that closely resembles the original TypeScript source code because es2015 supports classes. Private fields are a new feature in modern JavaScript specifications, but TypeScript can generate similar features using weak maps for older JavaScript runtimes. Finally, some modern JavaScript features cannot be transpiled to older JavaScript runtimes, and TypeScript will give an error if you try to compile such code.