Var with the difference 1.let
The scope is let block, var is a function of the scope of
2. Variable
Variable names consist of letters, numbers, underscores and $ symbols
3. Constant
Name all caps
4. naming
Categories: the first letter capitalized
Function names and variable names: lowercase first letter, written Camel
The basic types of
String ( '' or ''), numeric, boolean
6.null与underfined
null: has been defined, the variable is null
underfined: declared, not initialized
7. prevent bubbling, the default behavior
Prevent bubbling: event.stopPropagation ();
Prevent the default behavior: event.preventDefault ();
Uniform abbreviated as: return false
8. page response
9. Obtain node tag
document.getElementById (id); // Get node id tag
document.getElementByClassName (className) // Get node label className
document.getElementByTagName (tag) // Gets the label of nodes by tag name tag