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Parameters

Functions can now accept default parameters.
RESETRUNFULL
<!DOCTYPE html><html><body><script>

function f(a,b,c=10){
   console.log(a);
   console.log(b);
   console.log(c);}f(1,2);  // 1 2 10

</script></body><html>
An arbitrary number of parameters can now easily be passed and processed with the 'rest parameter'. Prefixed with ... , the 'rest parameter' must be the last formal parameter. Additional type checking can be performed with 'typeof'. Note that the ... operator is also applicable to an object and an iterable.
RESETRUNFULL
<!DOCTYPE html><html><body><script>

function f(a,b,...r){
   console.log(a);
   console.log(b);
   for (v of r) console.log(v);
   console.log(Array.isArray(r));}f(1,2,3,4,5);  // 1 2 3 4 5 true

</script></body><html>
Arguments can now be 'destructured' as they are passed into a function, following the same principles in 8.2.3 and 8.12.5.
RESETRUNFULL
<!DOCTYPE html><html><body><script>

function f({a,b:[c,d],e=100}){
   console.log(a);   //console.log(b); // ReferenceError
   console.log(c);
   console.log(d);
   console.log(e);}f({a:10,b:[20,30]});  // 10,20,30,100function g({a="foo",b}={}){
     console.log(a,b);};g({a:1,b:2}); // 1 2g(); // foo undefined

</script></body><html>
Javascript passes by value or reference. When a passed variable references an object such as an array, the value passed is a reference(memory address) to the object. Hence, a function can modify the properties of an object passed into it, but not the 'entire object as a whole' for the variable. Primitives are always passed by value.
RESETRUNFULL
<!DOCTYPE html><html><body><script>

function changeStuff(n, o1, o2){
   n = n * 10;
   o1.item = "changed";
   o2 = {item: "changed"};}var num = 10;var obj1 = {item: "unchanged"};var obj2 = {item: "unchanged"};changeStuff(num, obj1, obj2);console.log(num);        // 10 (unchanged)console.log(obj1.item);  // changedconsole.log(obj2.item);  // unchanged

</script></body><html>