Explanation of the basic methods of merging arrays in JavaScript_Basic knowledge

Here are two simple methods:
The first type

var mergeTo = [4,5,6], 
   mergeFrom = [7,8,9]; 
 
mergeTo = mergeTo.concat(mergeFrom); 
mergeTo; // is: [4, 5, 6, 7, 8, 9] 

or

var a = [1,2], b = [3,4], c = a.concat(b); 
 

The second type

var mergeTo = [4,5,6], 
var mergeFrom = [7,8,9]; 
 
Array.prototype.push.apply(mergeTo, mergeFrom); 
 
mergeTo; // is: [4, 5, 6, 7, 8, 9] 

Merge multiple arrays merge array:

// 特殊处理业务-必须启用 
var _SPECIAL_MUST_ENABLE_LIST = ['intime']; 
 
if(termNo != null && termNo.indexOf("9966") == 0){ 
  var newMustEnableList = ['mobile','psp','jtk','credit','train','bank','alipay','lottery','movie','littleTransfer', 
               'trafficFines','concert','mall','airplane','hotel','recycle']; 
  _SPECIAL_MUST_ENABLE_LIST = _SPECIAL_MUST_ENABLE_LIST.concat(newMustEnableList); 
}