第十七章 错误处理及调试

try {
  // 可能会导致错误的代码
} catch (error) {
  // 在错误发生时怎么处理
}

function testFinally() {
  try {
    return 2;
  } catch (error) {
    return 1;
  } finally {
    return 0;
  }
}

function CustomError(message) {
  this.name = "CustomError";
  this.message = message;
}

CustomError.prototype = new Error();
CustomError.prototype.constructor = CustomError;

throw new CustomError("This is a message!");

window.onerror = function(message, url, line) {
  alert(message);
  return false; // 阻止浏览器报告错误的默认行为
};

function addQueryStringArg(url, name, value) {
  if (url.indexOf("?") == -1) {
    url += "?";
  } else {
    url += "&";
  }
  url += encodeURIComponent(name) + "=" + encodeURIComponent(value);
  return url;
}

/**
 * 监听全局的js文件错误
 * @param {String}  message   错误信息
 * @param {String}  script    出错的文件
 * @param {String}  line      出错代码的行号
 * @param {String}  column    出错代码的列号
 * @param {Object}  errorObj  错误的详细信息，Anything
 */
window["onerror"] = function(message, script, line, column, errorObj) {
  _ins.error(
    normalizeError({
      message: message,
      name: !!errorObj && (errorObj.message || message.split(":")[1].trim()),
      script: script,
      line: line,
      stack: !!errorObj && errorObj.stack
    })
  );
  return true;
};

// Normalize Error objects across all browsers into something semi-standard.
// Not all properties are will be available, but if they are, they'll at
// least have a predictable property name.
function normalizeError(err) {
  var o = {
    message: err.message,
    script: err.fileName || err.sourceURL || err.script,
    name: err.name,
    line: err.lineNumber || err.line,
    stack: err.stackTrace || err.stack
  };

  // Chrome doesn't provide script/line # properties in Error objects, and
  // only reports the script/line # of where an error was last rethrown (as
  // opposed to the original throw point).  So we scrape the stack trace to
  // get that info
  if (
    window.chrome &&
    err.stack &&
    /(\w{3,5}:\/\/[^:]+):(\d+)/.test(err.stack)
  ) {
    o.script = RegExp.$1;
    o.line = RegExp.$2;
  }
  // Clear out undefined properties
  for (var k in o) {
    if (o[k] === null || o[k] === undefined) {
      delete o[k];
    }
  }
  return o;
}

Promise.resolve("a:1")
  .then(JSON.parse)
  .then(
    json => {
      console.log("不会执行到这里", json);
    },
    err => {
      //这儿捕获的是上一个JSON.parse时的错误
      console.log("上面err在这里被处理", err.message);
      //Unexpected token a
    }
  )
  .catch(err => {
    console.log("不会触发这个error", err);
  })
  .then(() => {
    console.log("任然执行");
  });

// 浏览器
window.addEventListener("unhandledrejection", e => {});
// nodejs
process.on("unhandledRejection", function(reason, promise) {
  console.log(reason); // [Error: unhandledrejection]
  console.log(promise); // Promise { <rejected> [Error: unhandledrejection] }
});