未捕获的TypeError:无法读取未定义的属性(读取“”indexOf“”)

let str;
console.log(str.indexOf('a')); // 这将导致错误

let str = '';
console.log(str.indexOf('a')); // 输出 -1

let obj = {};
console.log(obj.someProperty.indexOf('a')); // 这将导致错误

let obj = { someProperty: '' };
console.log(obj.someProperty.indexOf('a')); // 输出 -1

let data;
fetchData().then(response => {
    data = response;
    console.log(data.someProperty.indexOf('a')); // 这可能会导致错误
});

let data;
fetchData().then(response => {
    data = response;
    if (data && data.someProperty) {
        console.log(data.someProperty.indexOf('a')); // 安全访问
    }
});

function safeIndexOf(obj, prop, value) {
    if (obj && obj[prop]) {
        return obj[prop].indexOf(value);
    }
    return -1;
}

let obj = {};
console.log(safeIndexOf(obj, 'someProperty', 'a')); // 输出 -1

obj = { someProperty: '' };
console.log(safeIndexOf(obj, 'someProperty', 'a')); // 输出 -1

fetchData().then(response => {
    obj = response;
    console.log(safeIndexOf(obj, 'someProperty', 'a')); // 安全访问
});