Check out Javascript's Array API for details on the exact syntax for Array methods. Modifying your code to use the correct syntax would be:
var array = [];
calendars.forEach(function(item) {
array.push(item.id);
});
console.log(array);
You can also use the map() method to generate an Array filled with the results of calling the specified function on each element. Something like:
var array = calendars.map(function(item) {
return item.id;
});
console.log(array);
And, since ECMAScript 2015 has been released, you may start seeing examples using let or const instead of var and the => syntax for creating functions. The following is equivalent to the previous example (except it may not be supported in older node versions):
let array = calendars.map(item => item.id);
console.log(array);