javascript - 属性和子属性未定义检查

Question

这个问题已经有答案了:

Test for existence of nested JavaScript object key (64 个回答)

已关闭 3 年前。

我的代码中目前有这个 JavaScript 函数:

getCoverPhoto(item) {
  if (item != undefined && item.gallery != undefined && item.gallery[0] != undefined)
    return item.gallery[0].media;
  return "";
}

如何简化if条件如上？如果不能简化，是否可以写得更好？

Answer 1

例如使用三元运算符:

getCoverPhoto(item) {
  return item && item.gallery && item.gallery[0] ? item.gallery[0].media : '';
}

进一步阅读documentation :

The conditional (ternary) operator is the only JavaScript operator that takes three operands: a condition followed by a question mark (?), then an expression to execute if the condition is truthy followed by a colon (:), and finally the expression to execute if the condition is falsy. This operator is frequently used as a shortcut for the if statement.

或者使用ES6+:

const getCoverPhoto = item => item && item.gallery && item.gallery[0] ? item.gallery[0].media : '';

希望对您有所帮助!