Types of JavaScript Errors (Quick Check for Errors)

1. syntaxError syntax error

• Irregular variable names:
  var 1 = 1; // Uncaught SyntaxError: Unexpected number
var 1a = 1; // Uncaught SyntaxError: Invalid or unexpected number
• Keyword assignment:
  new = 1; // Uncaught SyntaxError: Unexpected token =
• Basic syntax error:
  var a = 5: // Uncaught SyntaxError: Unexpected token :

2. ReferenceError

• Variable or function is not declared:
  fn(); // Uncaught ReferenceError: fn is not defined
• When assigning a value to an object that cannot be assigned:
  console.log() = 2; // Uncaught ReferenceError: Invalid left-hand side in assignment

3. RangeError range error

• The array length is assigned a negative number:
  var arr = [1, 2, 3];
arr.length = -1; // Uncaught RangeError: Invalid array length
• Object method parameter out of feasible range
  var num = 66.66;
num.toFixed(-1); // Uncaught RangeError: toFixed() digits argument must be between 0 and 100

4. TypeError

• Call a method that doesn't exist:
  123(); // Uncaught TypeError: 123 is not a function
// Will first judge whether it may be a function, like 123, it cannot be a function, so the type error is reported directly, and if it is a legal function name, a ReferenceError is reported
var obj = {}
obj.say(); // Uncaught TypeError: obj.say is not a function
• Instantiate primitive values:
var a = new 1; // Uncaught TypeError: 1 is not a constructor

5. URIError URI error

URI: URIFORM RESOURCE IDENTIFIER  统一资源标识符
URL: URIFORM RESOURCE LOCATOR  统一资源定位符
URN: URIFORM RESOURCE NAME  统一资源标识符

URI包括URL和URN

decodeURI("%abc"); // Uncaught URIError: URI malformed

6. EvalError eval function execution error