JavaScript之数据类型转化
一.显示数据类型
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>数据类型转化</title> </head> <body> <div>100</div> </body> </html> <script type="text/javascript"> var oDiv = document.getElementsByTagName( 'div')[0]; alert(typeof oDiv.innerHTML ); </script>
二.数据类型转化方式
数据类型的转化
1.强制类型转化
Number():只能转换纯数字的字符串,不能转换非纯数字的字符串,会出现NaN
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>强制类型转换之Number</title> </head> <body> </body> </html> <script type="text/javascript"> var i = '100'; alert( Number(i) ); </script>
温馨小提示:如果字符串中含有非数字字符串,强制转换Number将出现NaN[not a number]
NaN是一个不是数字的数字类型;只要出现就证明我们的运算或者数据类型转换.
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>强制类型转换之Number</title> </head> <body> </body> </html> <script type="text/javascript"> var ii = '100px'; alert( Number(ii) ); </script>
支持小数转换:不过小数点后非0会切掉
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>强制类型转换之Number</title> </head> <body> </body> </html> <script type="text/javascript"> var iii = '100.01000'; alert( Number(iii) ); </script>
parseInt():可以转换不是纯数字的字符串,后面非数字的字符串不转换,其余数字字符串转换.意味着不能转换小数即:100.5也只能转换为100
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>强制转换类型之parseInt</title> </head> <body> </body> </html> <script type="text/javascript"> var i = '100px'; //有效转换的字符串 alert( parseInt(i)); //转换类型 alert( typeof parseInt(i)); </script>
温馨小提示:字符串起始是非数字的,转换时会出现NaN
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>强制转换类型之parseInt</title> </head> <body> </body> </html> <script type="text/javascript"> var ii = 'a100'; alert(parseInt(ii)); </script>
parseFloat():支持小数转换
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>强制类型转换之parseFloat</title> </head> <body> </body> </html> <script type="text/javascript"> var i = '100.9'; alert( parseFloat(i)); </script>
温馨小提示:起始位置是非数字字符串,转换时会出现NaN
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>强制类型转换之parseFloat</title> </head> <body> </body> </html> <script type="text/javascript"> var ii = 'a100.9'; alert( parseFloat(ii)); </script>
2.隐式类型转换
字符串和数字做加号,会转换成字符串
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>隐式转换</title> </head> <body> </body> </html> <script type="text/javascript"> var a = '100'; var b = 17; var c = a + b; alert(c); alert(typeof c); </script>
字符串和数字做减法会转换成数字
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>隐式转换</title> </head> <body> </body> </html> <script type="text/javascript"> var a = '100'; var b = 17; var c = a - b; alert(c); alert(typeof c); </script>
字符串和字符做减法会转换成数字
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>隐式转换</title> </head> <body> </body> </html> <script type="text/javascript"> var a = '100'; var b = '17'; var c = a - b; alert(c); alert(typeof c); </script>
/ ÷ * 号都成立
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>隐式转换</title> </head> <body> </body> </html> <script type="text/javascript"> var a = '100'; var b = '17'; var c = a * b; alert(c); alert(typeof c); </script>
字符串和字符串做++ --会转换成数字
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>隐式转换</title> </head> <body> </body> </html> <script type="text/javascript"> var a = '100'; var b = 17; var c = a + b; alert(a++); alert(typeof c); </script>
字符串和数字做> <比较,会转换为数字,进而量数字比较大小
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>隐式转换</title> </head> <body> </body> </html> <script type="text/javascript"> var q = '19'; var w = 100; alert(q>w); </script>
字符串和字符串进行大小比较,会按照字符串的方法:逐个比较
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>隐式转换</title> </head> <body> </body> </html> <script type="text/javascript"> var e = '19'; var r = '180'; alert(e>r); </script>
!
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>隐式类型转换!</title> </head> <body> </body> </html> <script type="text/javascript"> //0代表false var a = 0; //所以!a会进行隐式转换为true alert(!a); </script>
