Here’s a quick glimpse of all the TS10 features, that are part of the spec and have already been shipped with the latest version of Chrome:

1. Trim whitespaces only from start of a string

   " My String ".trimStart()
   
   // Produces:
   "My String "
   

2. Trim whitespaces only from end of a string:

   " My String ".trimEnd()
   
   // Produces:
   " My String"
   

3. Flatten an array:

   [1, 2, 3, [4, [5, 6]]].flat()
   
   // Produces:
   [1, 2, 3, 4, [5, 6]]
   

4. Flatten an array to depth of 2:

   [1, [2, 3], 4, 5, [6, [7 , 8]]].flat(2)
   
   // Produces:
   [1, 2, 3, 4, 5, 6, 7, 8]
   

5. Flatten the whole array:

   [1, 2, [3], [
     [[4, 5, 6]],
     [[[[7, 8]], 9]]
   ]].flat(Infinity)
   
   // Produces:
   [1, 2, 3, 4, 5, 6, 7, 8, 9]
   

6. Create objects from array like representation of the object:

   Object.fromEntries(
     [
       ["key1", "value"], 
       ["key2", 37]
     ]
   )
   
   // Produces:
   Object { key1: "value", key2: 37 }
   

7. Create objects from a map:

   Object.fromEntries(
     new Map([
       ["key1", "value"], 
       ["key2", 37]
     ])
   )
   
   // Produces:
   Object { key1: "value", key2: 37 }
   

8. Get symbol description from read-only property .description:

   const sym = Symbol('foo');
   console.log(sym.description);
   
   // Outputs:
   foo
   

9. Catch without the once-mandatory parameter in catch block:

   try {
     throw new Error("Some error");
   } catch {
     console.log('An error occured');
   }
   
   // Outputs:
   An error occured
   

10. Return source code of a function, verbatim, using toString() method:

    const fn = (param1, param2) => {
      console.log(param1, param2);
    }
    
    console.log(fn.toString())
    
    // Outputs:
    (param1, param2) => {
      console.log(param1, param2);
    }
    

11. Return all matches (and capturing group) of a string against given regular expression:

    const regexp = RegExp('l','g'); 
    const str = 'Hello world';
    let matches = str.matchAll(regexp);
    
    for (const match of matches) {
      console.log(match); 
    }
    
    // Outputs:
    Array ["l"]
    Array ["l"]
    Array ["l"]
    

12. Map then flatten the array using flatMap

    [1, 2, 3, 4].flatMap(elem => [elem * 2])
    
    // Produces:
    [2, 4, 6, 8]
    

Are these features ready to be used?

Well, some are and some are not. You can check for browser or nodejs compatibility by looking up features on MDN.

For example:

• Array.prototype.flat()^[1] is available in NodeJS 11, Chrome 69 and Firefox 62 and above.

Nevertheless these are some really interesting additions to JavaScript and more is on the way.

Links and more:

[1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat#Browser_compatibility

[2] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt

[3] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flatMap