var arr = ['apple', 'banana', 'orange'];
var str = arr.join(); // 默认用逗号分隔
console.log(str); // "apple,banana,orange"

var strWithSpace = arr.join(' '); // 用空格分隔
console.log(strWithSpace); // "apple banana orange"

var arr = [1, 2, 3];
var str = arr.toString();
console.log(str); // "1,2,3"

var arr = ['a', 'b', {name: 'John'}];
var str = JSON.stringify(arr);
console.log(str); // '["a","b",{"name":"John"}]'

var arr = ['q', 'jquery', 'ajax'];
var str = $.param({search: arr});
console.log(str); // "search%5B%5D=q&search%5B%5D=jquery&search%5B%5D=ajax"

var arr = ['a', {b: 2}];
console.log(arr.join()); // "a,[object Object]"
console.log(JSON.stringify(arr)); // '["a",{"b":2}]'

var numbers = [1, 2, 3];
var str = numbers.map(n => `Item ${n}`).join('; ');
console.log(str); // "Item 1; Item 2; Item 3"

var multiArr = [1, [2, [3]]];
console.log(multiArr.join()); // "1,2,3" - 会扁平化
console.log(JSON.stringify(multiArr)); // "[1,[2,[3]]]" - 保留结构