Top 10 JavaScript errors

Top 10 JavaScript errors

javascript errors

https://rollbar.com/blog/tags/top-errors

https://rollbar.com/blog/top-10-javascript-errors/

1. TypeError

2. RangeError

3. ReferenceError

4. SyntaxError

5. InternalError

6. URIError

7. Warning

8. EvalError

JavaScript Errors

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error

Uncaught TypeError: Cannot read property '...' of undefined

var foo;

foo.getName();
// Uncaught TypeError: Cannot read property 'getName' of undefined

foo.name;
// Uncaught TypeError: Cannot read property 'name' of undefined

Uncaught TypeError: Cannot read property 'length' of null

var obj = null;

obj.length;
//  Uncaught TypeError: Cannot read property '...' of null

undefined == null;
//true
undefined === null;
//false

CORS script error

// .htaccess
// Access-Control-Allow-Origin


// crossorigin="anonymous"

Uncaught TypeError: ... is not a function

var foo;

this.foo();
// Uncaught TypeError: this.foo is not a function

foo();
// Uncaught TypeError: foo is not a function

this & context error

The reason is that the anonymous function being executed is in the context of the document, whereas clearBoard is defined on the window.

function clearBoard(){
  alert("Cleared");
}

document.addEventListener("click", function(){
  console.log(`this`, this);
  // this === #document
  this.clearBoard();
});

window.addEventListener("click", function(){
  console.log(`this`, this);
  // this === Window
  this.clearBoard();
});

bind

var that = this; 
var self = this; 
// save reference to 'this', while it's still this!

document.addEventListener("click", function(){
  self.clearBoard();
  // that.clearBoard();
});

/ /Alternatively, in the newer browsers, you can use the bind() method to pass the proper reference:

document.addEventListener("click", this.clearBoard.bind(this));

Uncaught RangeError

Number.toExponential(digits) accept digits from 0 to 100

Number.toFixed(digits) accept digits from 0 to 100

Number.toPrecision(digits) accepts digits from 1 to 100.

new Array(-1);
// Uncaught RangeError: Invalid array length

var num = 2;

num.toExponential(-2);
// Uncaught RangeError: toExponential() argument must be between 0 and 100 at Number.toExponential 


// num.toFixed(101);
// Uncaught RangeError: toFixed() digits argument must be between 0 and 100 at Number.toFixed

num.toPrecision(0);
// Uncaught RangeError: toPrecision() argument must be between 1 and 100 at Number.toPrecision 

Number

Number.MAX_VALUE;
// 1.7976931348623157e+308

Number.MAX_VALUE + Number.MAX_VALUE;
// Infinity
Number.parseFloat(Infinity);
// Infinity


Number.MIN_VALUE;
// 5e-324

Number.MAX_SAFE_INTEGER;
// 9007199254740991

Number.MIN_SAFE_INTEGER;
// -9007199254740991

function local params empty bug

function 形参，实参

var testArray= ["Test"];

function testFunction(testArray) {
    for (var i = 0; i < testArray.length; i++) {
      console.log(testArray[i]);
    }
}
testFunction();

Uncaught TypeError: Cannot set property '...' of undefined

var foo;

foo.name = foo;
// Uncaught TypeError: Cannot set property 'name' of undefined

Uncaught ReferenceError: ... is not defined

xyz;
//  Uncaught ReferenceError: xyz is not defined

Errors on the world’s top 100 websites and how to avoid them

https://rollbar.com/blog/top-100-websites-errors/

HTTP error

TypeScript

1. JavaScript that scales.
2. TypeScript is a typed superset of JavaScript that compiles to plain JavaScript.
3. Any browser. Any host. Any OS. Open source.

https://www.typescriptlang.org/

refs

https://rollbar.com/error-tracking/javascript/

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