js basic data types: Number, String, Number, Null, Undefined, if you know these, just go ahead~
Convert data type to String
Conversion method 1: use the toString() method
Conversion method 2: use the String() function
let a = 123;
console.log(a.toString()) // '123'
let b = true
console.log(b.toString()) // 'true'
let c = null;
console.log(c.toString()) // 报错
let d = undefined
console.log(d.toString()) // 报错
let e = 123;
console.log(String(d)) // '123'
let f = true
console.log(String(f)) // 'true'
// null和undefined调用toString()或String()时不一样的
let g = null;
console.log(String(e)) // 'null'
let h = undefined
console.log(String(f)) // 'undefined'
Summarize:
1. Calling toString() and String() will return string type data without changing the original data type
2.toString() cannot convert null and undefined to strings. If you need to convert null and nudefined to strings, you can use String ()
Convert data type to Number type
Conversion method 1: use the Number() method
Conversion formula 2: use parseInt() method/parseFloat() method
let a = '123'
console.log(Number(a)) // 123
// 空字符串
let b = ''
console.log(Number(b)) // 0
let c = true
console.log(Number(c)) // 1
let d = false
console.log(Number(b)) // 0
let e = null;
console.log(Number(e)) // 0
let g = undefined
console.log(Number(g)) // NaN
// 如果纯数字和Number方法作用时一样的
let h = '123'
console.log(parseInt(h))
// 如果不是纯数字则只取整数数字
let i = '123.12px'
console.log(parseInt(h)) // 123
// parseFloat() 小数也会保留
let j = '1321.144px'
console.log(parseFloat(i)) // 1321.144
//如果对非String使用parseInt()获知parseFloat()
// 他会先将其转换成String然后再进行操作
let k = true
console.log(parseInt(k)) // NaN
let l = null
console.log(parseInt(l)) // NaN
let n = undefined
console.log(parseInt(n)) // NaN
Summarize:
1. The string of pure numbers is converted directly through the Number() function
2. If it is not a pure number and uses Number conversion, the type becomes NaN, but the data type is still number type
3. If there are spaces in the string, if there are no characters, it will be converted to 0
4. Boolean value to digital true is 1, false is 0
5. Null to digital null is 0
6. undefined is NaN
Two methods for special treatment of strings
parseInt()
1. The string effect on pure numbers is consistent with Number()
2. Non-pure numbers, if they do not start with English, only integer numbers are taken
3. Non-pure numbers, starting with English is NaN
4.parseInt() can be used to take an integer
pressFloat()
1. The string effect on pure numbers is consistent with Number()
2. Non-pure numbers, all numbers will be taken if they do not start with English
3. Non-pure numbers, starting with English is NaN
Convert data type to Boolean
Conversion method: use Boolean()
let a = 123
console.log(Boolean(a)) // true
let b = -123
console.log(Boolean(b)) // true
let c = 0
console.log(Boolean(c)) // false
let d = NaN
console.log(Boolean(d)) // false
let e = 'test'
console.log(Boolean(e)) // true
let f = ''
console.log(Boolean(f)) // false
let g = null
console.log(Boolean(g)) // false
let h = undefined
console.log(Boolean(h)) // fasle
// 对象也为true
let i = {
name: '法外狂徒',
age: 22
}
console.log(Boolean(i)) // true
Summarize:
1. Number type to Boolean type: except 0 and NaN, the rest are true
2. String type to Boolean type: except for the empty string, the rest are true
3. Both null and undefined will be converted to false
4. The object will also be converted to true
Conclusion:
There are only a few types of data in js, but it is still a bit of a pain in the head to turn around the type. Familiarity with the conversion of data types will allow us to avoid some minor problems when writing code. Everyone usually writes bugs Pay more attention to it, it is still no problem, friends, come on, I wish you all the best in your work~
The above is just my personal opinion, please correct me if there are any mistakes, thank you~