Cannot read property 'push' of undefined when combining arrays

Question

When pushing an array\'s contents to another array I get

\"Uncaught TypeError: Cannot read property \'push\' of undefined\" error in this snippet.

Answer 1

This error occurs in angular when you didn't intialise the array blank.
For an example:

userlist: any[ ];
this.userlist = [ ]; 

or

userlist: any = [ ];