JavaScript bijiao
bijiao huo luo ji yun suo yu ce shi true huo false。
bijiao yun suo
bijiao yun suo zai luo ji yu ju zhong shi yong, yi pan ding bian liang huo zhi ji shi fu xiang deng.
women ding gai x = 5, xia pang bao shi bijiao yun suo:
| yun suo | shu mo | bijiao | hui fan | 测试 |
|---|---|---|---|---|
| == | deng yu | x == 8 | false | 试一试 |
| x == 5 | true | 试一试 | ||
| x == "5" | true | 试一试 | ||
| === | zhi ji xiang deng qi lei xing xiang deng | x === 5 | true | 试一试 |
| x === "5" | false | 试一试 | ||
| != | bu xiang deng | x != 8 | true | 试一试 |
| !== | zhi ji bu xiang deng huo lei xing bu xiang deng | x !== 5 | false | 试一试 |
| x !== "5" | true | 试一试 | ||
| x !== 8 | true | 试一试 | ||
| > | > | da yu | false | 试一试 |
| < | xia yu | x < 8 | true | 试一试 |
| >= | da yu huo deng yu | x >= 8 | false | 试一试 |
| <= | xia yu huo deng yu | x <= 8 | true | 试一试 |
ruo shi yong
bijiao yun suo ke yong zai tiao jian yu ju zhong dui zhi jian bijiao, gen ju jie guo qiang tai dong wu:
if (age < 18) text = "tai nian qing";
ben jiao cheng xia ge zhang jie zhong, ni xiang xue dao geng duo guan yu tiao jian yu ju de zhi shi.
luo ji yun suo
luo ji yun suo yu yong yu pan ding bian liang huo zhi jian de luo ji.
women ding gai x = 6 qi y = 3, xia pang bao shi luo ji yun suo:
| yun suo | shu mo | li pi | 测试 |
|---|---|---|---|
| && | yu | (x < 10 && y > 1) wei zhen | 试一试 |
| || | huo | (x == 5 || y == 5) wei false | 试一试 |
| ! | fei | !(x == y) wei zhen | 试一试 |
tiao jian (san yuan) yun suo
JavaScript ye bao han ke ji yu zhen ti tiao jian xiang bian liang fu zhi de tiao jian yun suo.
yu fa
bing fen ming = (tiao jian) ? value1:value2
shi li
var voteable = (age < 18) ? "tai nian qing":"zui gou cu shen";
Idan dake ga 18 ka dake kai, dake ga 'age' zhi ji xiao yu 18, dian liang 'voteable' de zhi jing shi 'tai nian qing', fei zhi dian liang 'voteable' de zhi jing shi 'zui gou cu shen'.
比较不同的类型
比较不同类型的数据也许会出现不可预料的结果。
如果将字符串与数字进行比较，那么在做比较时 JavaScript 会把字符串转换为数值。空字符串将被转换为 0。非数值字符串将被转换为始终为 false 的 NaN。
| 案例 | 值 | 测试 |
|---|---|---|
| 2 < 12 | true | 试一试 |
| 2 < "12" | true | 试一试 |
| 2 < "Bill" | false | 试一试 |
| 2 > "Bill" | false | 试一试 |
| 2 == "Bill" | false | 试一试 |
| "2" < "12" | false | 试一试 |
| "2" > "12" | true | 试一试 |
| "2" == "12" | false | 试一试 |
当比较两个字符串时，"2" 大于 "12"，因为（按照字母排序）1 小于 2。
为了确保正确的结果，在比较值前应该把变量转换为合适的类型：
age = Number(age);
if (isNaN(age)) {
voteable = "输入错误";
} else {
voteable = (age < 18) ? "太年轻" : "足够成熟";
}
