灏天阁

错误处理

· Yin灏

语法错误

let v01 = 100, v02 = 230;
let result = 0;


try {
  eval('result = v01 -- v02 ;')
} catch(err) {
  console.log(err); // SyntaxError: Unexpected identifier at index.js:6

  console.log(typeof err); // 'object'

  console.log(err instanceof SyntaxError); // true

  console.log(err.name); // SyntaxError
  console.log(err.message); // Unexpected identifier
  console.log(err.stack); // SyntaxError: Unexpected identifier at index.js:6
}

数据类型错误

js 引擎无法顺利转换特定操作数据的数据类型时，便会产生数据类型的错误。

let v01 = 100, v02 = 230;

let result = 0;

try {
  result = v01.replace('0', '1');
  console.log(result);
} catch(err) {
  with(console) {
    log(err); // v01.replace is not a function
    log(typeof err);
    log(err instanceof TypeError); // true

    log(err.name); // TypeError
    log(err.message); // v01.replace is not a function
    log(err.stack); // TypeError: v01.replace is not a function
  }
}

评估错误

js 引擎现今只能通过内置函数或者语句，才会产生评估错误。

try {
  throw new EvalError('Equation evaluation error occurs!');
} catch(err) {
  with(console) {
    log(err); // EvalError: Equation evaluation error occurs!
    log('\n');

    log(typeof err); // object
    log(err instanceof EvalError); // true
    log('\n');

    log(err.name); // EvalError
    log(err.message); // Equation evaluation error occurs!
    log(err.stack); // EvalError: Equation evaluation error occurs!
  }
}

范围错误

js 引擎评估到特定数据范围以外的数据时，便会产生数据范围错误。

var value = 200;
let list = null;
let result = 0;

try {
  result = value.toPrecision(101);
  list = new Array(-3);
  console.log(result);
} catch(err) {
  with(console) {
    log(err); // RangeError: toPrecision() argument must be between 1 and 100 at Number.toPrecision (<anonymous>)
    log('\n');

    log(typeof err); // object
    log(err instanceof RangeError); // true

    log('\n');
    log(err.name); // RangeError
    log(err.message); // toPrecision() argument must be between 1 and 100
    log(err.stack); // RangeError: toPrecision() argument must be between 1 and 100 at Number.toPrecision (<anonymous>)
  }
}

引用错误

尚未被声明的变量名称，被引用，会产生引用错误。

let v01 = 100, v02 = 150;
let result = 0;

try {
  result += v01 + v03;
  console.log(result);
} catch(err) {
  with(console) {
    log(err); // ReferenceError: v03 is not defined
    log('\n');

    log(typeof err); // object
    log(err instanceof ReferenceError); // true

    log('\n');
    log(err.name); // ReferenceError
    log(err.message); // v03 is not defined
    log(err.stack); // ReferenceError: v03 is not defined
  }
}

网址在编码或解码上的错误

js 引擎无法顺利对特定网址进行编码会解码时，便会产生 URI 错误，引申为网址在编码或解码上的错误。

try {
  decodeURIComponent('https://tw.dictionary.yahoo.com/dictionary?p=%E8%81%96%E8%AA%95%E7%AF%FF')
} catch(err) {
  with(console) {
    log(err); // URIError: URI malformed at decodeURIComponent (<anonymous>)
    log('\n');

    log(typeof err); // object
    log(err instanceof URIError); // true

    log('\n');
    log(err.name); // URIError
    log(err.message); // URI malformed
    log(err.stack); // URIError: URI malformed at decodeURIComponent (<anonymous>)
  }
}

逻辑错误

js 引擎无法察觉，编程人员思考不够周全导致的逻辑错误。

let num_list = Array.from(new Array(11), (value, index) => parseInt(100 * Math.random()));

let result = null;

result = Math.min(...num_list);

console.log(num_list);
console.log(result);

console.log(`The maximum value is ${result}.`);

let radius = 55;

result = (3 / 4 * Math.PI * radius ** 3).toFixed(3);

console.log(`The sphere volume of radius ${radius} is ${result}`);

处理特定异常错误

程序员重新定义错误，成为用户可以理解或不会看见的错误信息。

try {
  // throw new URIError('Defined error message here...')
  throw 'Logical error occurs';
} catch(err) {
  console.log(err.name);
  console.log(err.message);
  console.log(err.stack);
} finally {
  console.log('Message after exception handling.');
}

调试机制

js 引擎支持两种调试机制：

  1. 严格模式（use strict）
  2. debugger

严格模式

js 引擎处于严格模式下，对源码的语法要求是相当严格的。

"use strict";

try {
  let v01 = 100;
  var v02 = 250;
  v03 = 600;
} catch(err) {
  console.log(err); // ReferenceError: v03 is not defined
}

function fun01() {
  radius = 10;
  return 4 * Math.PI * radius ** 2;
}

try {
  fun01();
} catch (err) {
  console.log(err); // ReferenceError: radius is not defined
}

try {
  eval('\
    with(Math)\
    {\
      console.log(PI);\
    }')
} catch (err) {
  console.log(err); // SyntaxError: Strict mode code may not include a with statement
}

try {
  let num01 = 0;
  eval('num01 = 0377;')
} catch (err) {
  console.log(err); // SyntaxError: Octal literals are not allowed in strict mode.
}

try {
  let person = {name: 'Jasper', gender: 'male', age: '33'};
  eval('delete person;')
} catch (err) {
  console.log(err); // SyntaxError: Delete of an unqualified identifier in strict mode.
}

源代码的断点设置和逐句执行

let radius = 10, height = 15;
let result = 0;

result = Math.PI * (radius ** 2) * height;
console.log(result);

debugger;

result = 2 * Math.PI * radius ** 2 + 2 * Math.PI * radius * height;
console.log(result);

debugger;

result = 4 / 3 * Math.PI * radius ** 3;
console.log(result);
debugger;

result = 4 * Math.PI * radius ** 2;
console.log(result);

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