Interview Questions---Miscellaneous

After a period of sorting, I have selected interview questions to share with my friends~ Let's take a look at the following interview questions!

first question:

var lowerCase = /^[a-z]+$/;
console.log(lowerCase.test(null));//true
console.log(lowerCase.test());//true

Friends who are familiar with regular expressions in javascript should all understand that this is a regular expression that validates any a to z. The test() method in the regular expression verifies a string, and null is an object, which is forced to be converted to a string when using the test() method, so it is true; when the verification value is empty, it is forced to be converted to test (' undefined'), so also true;

Second question:

var a = /123/;
var b = /123/;
console.log(a==b);//false
console.log(a===b);//false

This question requires a certain understanding of object. The object is compared by the memory address pointed to by the pointer. As long as the memory address is different, both are false; in this question, both a and b are regular objects, pointing to a and b respectively, So the memory pointed to is not the same, it is false;

Third question:

console.log(1<2<3,3<2<1);//true,true

Whether it is '<', or '>', it is operated from left to right; 1<2----true, true<3 will force true to convert to 1, that is, it becomes 1<3, so it is true ;

Similarly, 3<2 is false, and false<1 is converted to 0<1, so it is true;

Fourth question:

var arr = Array(3);
arr[0] = 2;
arr.map(function(elem){
    return '1';
})//['1',empty*2]

First of all, we need to understand the usage of map() function,

array.map(function(currentValue,index,arr){},thisValue);

①, each element in the array will execute this function, the function must pass

②, function parameters: currentValue is a required parameter , the value of the current element; index: optional, the index value of the current element; arr: optional, the array object to which the current element belongs

Fifth question:

function foo()    
}
var oldName = foo.name;
foo.name = "bar";
console.log(oldName,foo.name)//foo,foo

Note: The function instance will have a built-in name attribute. Because it is rarely used in development, many small partners do not know the existence of this thing. This attribute is read-only and cannot be modified. No matter how it is assigned, it is invalid. .

Question 5: Many friends must have used the method in Math. Next, let’s take a look at the interesting question. I didn’t find it before, so I will share it with you now~

var min = Math.min ();
var max = Math.max();
min < max

Comparing the minimum value and the maximum value, I believe that many friends feel like they will return true like stinky, but it is not true~

Math.min() and Math.max(), these two methods, if you pass them multiple arguments, are known to return the max/min value among them. However, if no parameters are passed, there will be a very interesting phenomenon: the return value of Math.min() is Infinity (positive infinity), and the return value of Math.max() is -Infinit (negative infinitesimal). So, the correct comparison result is Math.min() > Math.max().

Okay, my friends, that's all for today's interview questions~~~