Vue [difference] var / let / const of

where       

• Declare variables     
• No district-level scope     
• Can be pre-parsed       
• You can repeat the definition
• Declare global variables belonging to the top-level object (window) properties

let         

• Declare variables     
• There are block-level scope       
• No pre-parsed         
• The definition can not be repeated
• Declare global variables are not top-level object (window) properties

const   

• Statement read-only constants, once the declaration can not be changed       
• There are district-level scope       
•  No pre-parsed           
• The definition can not be repeated         
• Otherwise it must be assigned an error when defining
• Declare global variables are not top-level object (window) properties