七爪源码：让我思考的 JavaScript 面试问题 我真的了解 JavaScript 吗

JavaScript 最让我惊讶的部分是它周围总是有新事物发生。 而且，无论您对它了解多少，您都将始终了解有关它的新事物。

这些问题我收集了很长时间。 在大多数问题中，我真的不知道输出会是什么，直到我自己尝试了它们。

所以在这里我将它们记录下来，以便其他人可以利用它来学习新概念：

输出：

21
{name: “Lydia”} // age won’t be included. Because property defined with defineProperty are non enumerable by default.

输出：

false // delete operator only deletes a key in object
true // when we don't use any declaration before any variable, it will be treated as a global variable, and will be added as deletable entity in window object.undefined

输出：

[ { name: "Noren Red"} ] Initially I thought it will log [ null ] because we have initialised person with nullBut in reality, we are only setting new reference to person variable. Previous reference will be used in members arrayIn Short, { name: "Noren Red"} lives in some memory space whose address is X201and this is how referencing is workinglet person = X201
const members = [ X201 ]
person = null

输出：

Silver Surfer Because when we return a property, the value of the property is equal to the returned value, not the value set in the constructor function.

输出：

With the padStart method, we can add padding to the beginning of a string.
 
The value passed to this method is the total length of the string together with the padding. The string "Silver Surfer" has a length of 13. name.padStart(14) inserts 1 space at the start of the string, because 13 + 1 is 13. If the argument passed to the padStart method is smaller than the length of the array, no padding will be added.

输出：

777If we pass string and number combination to parseInt, what parseInt does is, it check at which position wrong datatype is getting started, if value before the wrong datatype is a valid number, it will return the valid number.

输出：

1 2 and undefined 3 and undefined 4 
If we don't pass initial value, then by default x will be first value of array, and y will be second value of array.

输出：

one - ["", " is ", " years old"]
two - Thor
three - 1000one - ["hey there, are you amazed"]
two - undefined
three - undefinedIf we use tagged template literals, the value of the first argument is always an array of the string values.The remaining arguments get the values of the passed expressions!

输出：

1
undefined
2

输出：

function // Classes in JS are functions under the hood

关注七爪网，获取更多APP/小程序/网站源码资源！