1)5种原始数据类型:Undefined、Null、Boolean、Number和String。需要注意的是JS中字符串属于原始数据类型。 2)typeof运算符:查看变量类型,对变量或值调用typeof运算符将返回下列值之一: undefined – 如果变量是 Undefined 类型的 boolean – 如果变量是 Boolean 类型的 number – 如果变量是 Number 类型的 string –...
toFixed 把数字转换为字符串,结果的小数点后有指定位数的数字。 toExponential 把对象的值转换为指数计数法。 toPrecision 把数字格式化为指定的长度。 valueOf 返回一个 Number 对象的基本数字值。 6. Boolean 对象 属性 属性 描述 constructor 返回对创建此对象的 Boolean 函数的引用 prototype 使您有能力向对象添加...
lastName){ greetingMsg = greetingMsg + firstName + " " + lastName; } return { sendGreeting: function(firstName, lastName){ msgTo(firstName, lastName); } getMsg: function(){ return greetingMsg; } } } const createMsg = sayHello(); createMsg.send...
“Control character in string: {a}.” : “在字符串中出现了Control的字符”, “Avoid \\’.” : “避免 \\”, “Avoid \\v.” : “避免 \\v”, “Avoid \\x-.” : “避免 \\x-”, “Bad escapement.” : “错误的转义字符”, “Bad number ‘{a}’.” : “错误的数字 ‘{a}’”...
// Assume the caller wants to pass in an array where the first index is the left // eye, and the 2nd is the right if (Array.isArray(eyes)) { return { left: eye[0], right: eye[1] } } // Assume that the caller wants to use a number to indicate that both eyes have the ex...
',database:'traindb',user:'train',password:'train'});constguessNumberDao={addGurssNumberResult:function(data){connPool.execute('insert into guess_his (guess_time, input_val, result_desc) values (?, ?, ?)',[newDate(),data.input_val,data.result_desc]);}};module.exports=guessNumber...
Examples of number literals are 0, 1, 2, 0.5, 0.00123 and so on and so forth. Number literals create number primitives, i.e numeric values that don't have any properties/methods attached to them. Consider the following code: JavaScript var x = 50.5; Here we create a variable x and th...
> Number(null) 0 parseFloat()parses the empty string asNaN: > parseFloat('') NaN > Number('') 0 parseFloat()parses until the last legal character, meaning you get a result where you may not want one: > parseFloat('123.45#')
number representing the character. For example, a space is returned as "%20." Edge Core Javascript Guide: The escape and unescape functions let you encode and decode strings. The escape function returns the hexadecimal encoding of an argument in the ISO Latin character set. The unescape ...
Get thefirstcharacter in a string: lettext ="HELLO WORLD"; letletter = text.charAt(0); Try it Yourself » Get thesecondcharacter in a string: lettext ="HELLO WORLD"; letletter = text.charAt(1); Try it Yourself » Get thelastcharacter in a string: ...