- Comparisons
- == double equals
- check for equality of value, but not equality of type
- it coerces both values to the same type and then compares them
- this can lead to some unexpected results.
- 0 == ' '; //true
- 0 == false; //true
- null == undefined; //true
- === triple equals. checks for equality of value and type
- 2 === '2'; //false
- false === 0; //false
- 10 !== '10' ; //ture
- 10 != '10'; //false
- console.log(). prints arguments to the console
- Running code from a file
- write code in a .js file and inculde the script in a .html file(abover the closing body tag)
-
"hi".toUpperCase(); //won't show up in the console
console.log("hi".toUpperCase()); //will show up in the console.
- conditions
- if
- else if
- else
- nesting(多种条件语句嵌套)
- TRUTHY AND FALSY VALUES
- all js values have an inherent truthyness or falseness about them
- false values:
- false
- 0
- ''''(empty string)
- null
- undefined
- NaN
- everything else is truthy!
- Logical Operations
- &&. AND
- ||. OR
- ! NOT
- ! null //true
- ! (0 === 0) //false
- ! (3 <= 4). //false
- How to check a string includes space or not?
if(string.indexOf(" ") === -1){
console.log("no space");
}
- 控制台基本操作
-
alert("hello, welcome to my world!!!") //在网页面出现弹框
prompt("please introduce yourself~") //在网页出现输入框,用户可以输入
"Peiyu Li"
let userInput = prompt("name")
userInput
"Peiyu"
parseInt("78") //字符转换成数字
78
parseInt("78dhkshdk")。 //字符转换成数字,自动滤去非数字部分
78
console.log("Good morning!!!")。 //输出,相当于print
Good morning!!!