Difference between JavaScript and Java

When declaring a variable, prefix the variable name with var.
Numbers of primitive data types are floating-point.
How to create an array
for in statement
JavaScript can pass a function to another function as an argument. (Since Java 8, Java can also give a lambda expression as an argument)

We have already confirmed 1 and 2.

Arrays created using [] provide indexes.

var arr = [1, 2, 3, 4, 5];
var sum = 0;
for (var i = 0; i < arr.length; i++) {
  sum = sum + arr[i];
}
alert('SUM:' + sum);

Arrays created using Array object provide indexes.

var arr = new Array(1, 2, 3, 4, 5);
var sum = 0;
for (var i = 0; i < arr.length; i++) {
  sum = sum + arr[i];
}
alert('SUM:' + sum);

Associative arrays have the form {key:value} and do not provide indexes. Java has no Associative arrays.

var person = {"name":"El Draque", "job":"pirate"};
alert(person.name);
alert(person["name"]);
alert(person.job);
alert(person["job"]);

You can access all elements of associative arrays with the for-in statement.

var person = {"name":"Barbadosed", "job":"pirate"};
var result = "";
for(var property in person) {
  result += person[property];
}
alert(result);

function x(a, y) {
  var ret = y(a);
  alert(ret);
}
function z(a) {
  return a * a
}
x(2, z);