|-运算符
|--基础运算符 + - * / %
|----加号:数字的求和、字符串的拼接
|----减号:数字的减法、对数字取反
|----乘法、除法、取余
var a = 10; var b = 10; var c = a + b; var d = "hello "; var e = "world"; alert(c); alert(a + d); alert(d + e);
|--复合运算 += -= *= /= %=
var f = "10";
f = f + 2; f += 2; alert(f);
|-自增自减 ++ --
|--注意位置a = b++;(先赋值再自加) a = ++b;(先自加再赋值)
var g = 5; g++; g = g + 1; g += 1; alert(g); var h = g++; h = g;(先执行) g++;(再执行) alert(h); var k = ++g; g++;(先执行) k = g;(再执行) alert(k);
|--关系运算符 > < >= <= !=(不等于) == (只判断数字,字符串类型的数字会当作数字型来判断) ===(会判断字符的类型)
var l = 3 >= 2; var p = 123; var q = "123"; alert(l); alert(p != q); alert(p !== q ); alert(p == q); alert(p === q );
|--逻辑运算符
|----逻辑非 ! (not)
var aa = 2; var bb = 3; var cc = !(aa >= bb); alert(cc);
|----逻辑与 && (and)
var dd = 2 >= 3; /*flase*/ var ee = 4 >= 1; /*/true*/ alert(dd && ee);
|----逻辑或 || (or)
var dd = 2 >= 3; /*flase*/ var ee = 4 >= 1; /*/true*/ alert(dd || ee);
|--三元运算符 条件?值1(true):值2(false)
var bl = 2>=1?"对":"错"; alert(bl);
var spmc = prompt("请输入商品名称"); var spmc = spmc == "鸡块"?"请给我10元":spmc == "汉堡"?"请给我15元":spmc == "可乐"?"请给我5元":"请输入正确的商品"; alert(spmc);