摘要：搬家篇二數(shù)據(jù)類型分為基本數(shù)據(jù)類型和引用數(shù)據(jù)類型基本數(shù)據(jù)引用數(shù)據(jù)當(dāng)，小數(shù)點(diǎn)后大于等于位時(shí)會自動轉(zhuǎn)換成科學(xué)計(jì)數(shù)法當(dāng)，當(dāng)整數(shù)部分大于等于位時(shí)會自動轉(zhuǎn)換成科學(xué)計(jì)數(shù)法。

搬家篇二

參數(shù)為Number類型時(shí)：能正確輸出；

console.log(Number(1));        //1
console.log(Number(1e-7));    //1e-7
console.log(Number(0b111));  //7
console.log(Number(NaN));   //NaN

參數(shù)為Boolean類型時(shí)：true->1;fasle->0；

console.log(Number(true));  //1
console.log(Number(false)); //0

參數(shù)為undefined時(shí)：其值為NaN

console.log(Number(undefined)); //NaN

參數(shù)為null時(shí)：

console.log(Number(null));    //0

參數(shù)為String類型時(shí)：

//數(shù)字字符串
console.log(Number("123"));   //123
console.log(Number("-123"));  //-123
console.log(Number("12.3"));  //12.3
console.log(Number("1e-7"));  //1e-7
console.log(Number("0xff"));  //255
console.log(Number("00123")); //123    
console.log(Number("   123")); //123
console.log(Number("	
123")); //123

//數(shù)字+字符或全字符字符串
console.log(Number("a123"));  //NaN
console.log(Number("false")); //NaN
console.log(Number("a123"));  //NaN

//空串或者空格字符串
console.log(Number("	
"));   //0
console.log(Number("  "));     //0
console.log(Number(""));       //0

參數(shù)類型是對象時(shí)：先進(jìn)行.valueOf(),如得到的時(shí)對象再進(jìn)行toString()，待得到基本數(shù)據(jù)類型為止，例如{}.valueOf().toString() = "[object Object]" 最后number的結(jié)果就是NaN了

console.log(Number({}));  //NaN
console.log(Number([1])); //1
console.log(Number([1,2]));  //NaN
cosole.log(Number([]));    //0

流程是：先String(x)變?yōu)樽址賹⒃撝狄詙進(jìn)制為基底轉(zhuǎn)為十進(jìn)制數(shù)，不填著為10，y的范圍： [2,36]

x參數(shù)為number時(shí)：值得注意??的是0.001,1e-7類型的值，會舍去小數(shù)點(diǎn)(e)后面的數(shù)值，返回前面的。

console.log(parseInt(123));   //123
console.log(parseInt(1e-7));  //1
console.log(parseInt(0xff));  //255
console.log(parseInt(NaN));   //NaN
console.log(parseInt(0.00001)); //0

x參數(shù)為boolean，undefined,null時(shí)：

console.log(parseInt(true));  //NaN
console.log(parseInt(false)); //NaN
console.log(parseInt(undefined)); //NaN
console.log(parseInt(null));    //NaN

x參數(shù)為String類型時(shí)：需要注意的時(shí)空串，空格字符串，數(shù)字+字符

console.log(parseInt(""));   //NaN
console.log(parseInt("-123"));  //-123
console.log(parseInt("  "));  //NaN
console.log(parseInt("	
"));   //NaN
console.log(parseInt("a123")); //NaN
console.log(parseInt("123a")); //123

參數(shù)x為對象時(shí)：同理通過.valueOf(),如得到的時(shí)對象再進(jìn)行toString()，待得到基本數(shù)據(jù)類型為止，然后按上述規(guī)則進(jìn)行輸出

console.log(parseInt({1:2}));   //"[object Object]"->NaN
console.log(parseInt([]));      //""->NaN
console.log(parseInt([1,2]));   //"1,2"->//1

帶參數(shù)x,y，當(dāng)y為0，null，undefined,NaN時(shí),會將y忽略默認(rèn)為10，超過[2,36]的范圍時(shí)返回NaN，當(dāng)x值無妨被y進(jìn)制表示時(shí)返回NaN，其余能表示幾位就幾位

console.log(parseInt("f",2));   //NaN
console.log(parseInt("11f",2);  //3
console.log(parseInt("123",37)); //NaN
console.log(parseInt("0xff",0));  //255
console.log(parseInt("0xff",NaN)); //255
console.log(parseInt("ff",[]));  //NaN

console.log(parseFloat(0xff));  //255
console.log(parseFloat("0xff"));  //0  
console.log(parseInt("0xff"));   //255  個(gè)人猜測parseInt(x,y)有y的存在所以能正確輸出
console.log(parseFloat(1e22));   //1e22
console.log(parseFloat(1e-7));   //1e-7
console.log(parseFloat("00123"));  //123
console.log(parseFloat(" "));     //NaN

第一：undefined, null沒有toString()屬性只能通過String(undefiend)

第二：y.toString(x), 的意思是將目標(biāo)數(shù)值y轉(zhuǎn)為x進(jìn)制的數(shù)值

console.log(String(null));  //"null"
console.log(0xff.toString(2));  //"11111111"
console.log(oxff.toString()); //"255" 不填默認(rèn)10進(jìn)制