The difference between apply, call and bind

Their role is to this Bind to the specified object .（ change this The direction of ）

• apply Take two parameters , The first parameter specifies the body of the function this The direction of the object , The second parameter is a subscript set , This set can be an array , It can also be an array of classes ,apply Method passes the elements in this collection as parameters to the called function .
• call The number of parameters passed in is not fixed , Follow apply The same thing , The first parameter also represents the inside of the function this Point to , When the first parameter is null、undefined when , The default point to window; Starting with the second parameter , Each parameter is passed into the function in turn .
• bind Function allows you to pass in the required this Bound object , And optionally pass in all or part of the formal parameters , Then return a new function （ Original function changed this Function pointed to ）