javascript - js 如何通过 try catch 正确使用 block 级变量

Question

假设以下代码:

   let test = dbCall();
    console.log(test);

现在我想将 dbcall 包装在 try catch 中。哪种方式更好:

let test = null;
try{
    test = dbCall();
} catch(e) {
    console.log(e);
}
console.log(test);


try{
    var test = dbCall();
} catch(e) {
    console.log(e);
}
console.log(test);

Answer 1

如果您想处理返回并引发自定义错误:

var test = dbCall();

try { 
    if(test == <dbCall_error_state>) throw "Custom error here.";
}
catch(e) {
    alert("Error: " + e);
}

PS 您需要将 'dbCall_error_state' 替换为 dbCall 的返回错误。

如果你想直接抛出dbCall()返回的错误，符合ECMAScript规范:

try {
    dbCall(); // may throw three types of exceptions
} catch (e) {
    if (e instanceof TypeError) {
        // statements to handle TypeError exceptions
    } else if (e instanceof RangeError) {
        // statements to handle RangeError exceptions
    } else if (e instanceof EvalError) {
        // statements to handle EvalError exceptions
    } else {
       // statements to handle any unspecified exceptions
       logMyErrors(e); // pass exception object to error handler
       alert("Error: " + e); // or alert it
    }
}

您可以在此处查看有关此内容的详细信息: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Statements/try...catch