Interview questions

1. 1px Fine line problem ===> I said iphone6 For example ： His dpr by 2, One logical pixel is equal to two physical pixels , When your logical pixel is 1 When , He will use one internally 22 Physical pixels to fill , So you can zoom 0.5 To solve this problem , He asked me if I could 0.1 0.2 0.3 0.4？ This is through dpr To the , If it is a double graph, zoom 0.5, If it is a triple graph, zoom 0.333 To achieve . Generally, it is a double graph , Because the double image will not be distorted on the double mobile phone , On three times the mobile phone, although he can use 33 Physical pixels to fill , But users can accept . If it is a triple graph , It will be clearer on the mobile phone with the double picture , But users will consume more traffic , So it's usually a double graph , Some companies just judge your mobile phone , Then use three times Or twice
2. meta What are the attributes of the tag ？ ===> name content http-equiv
3. header What labels are there in the head / ===> meta title Set character set Viewport width Etc., etc.
4. Deconstruct assignment , hypothesis let obj={name=” Pan Chenyang “,age=18},let {name,age} = obj, I print name and age Pan Chenyang can appear 18, But I first like deconstruction haha, But I want to print out what Pan Chenyang should do , Sure let {name:haha,age} = obj, perhaps let {name,age,…haha} = obj Take it like this
5. let and const const Can the defined variables really not be changed ？ ===> Basic data types are not good , Complex data types can be changed , Because it is the same address value .
6. I have an array bidirectional data binding , I changed the array , Why is the view not updated ？ ===> because js The reason for the mechanism , If you change the array by index or length , The view will not be updated , But the data will change . If you want the view to change ： Can pass Vue.set(target,index/propsname,value) Method to solve , Or use the compilation method of array , Or you can use forced update vm.$forceupdate, He only affects the instance itself , Not all the subcomponents

function Foo() {
    
    getName = function () {
     alert (1); };
    return this;
}
Foo.getName = function () {
     alert (2);};
Foo.prototype.getName = function () {
     alert (3);};
var getName = function () {
     alert (4);};
function getName() {
     alert (5);}

// Please write the following output ：
Foo.getName();
getName();
Foo().getName();
getName();
new Foo.getName();
new Foo().getName();
new new Foo().getName();