== 不检查类型，只检查值。 在javascript里面： null, undefined, false, '' 的值都是false 如果是 undefined的值是false的话 那么if(a==false)测试结果该是相等的,我测试的结果不是相等的. 但是 if(a==undefined) 结果却是相等的 http://www.ecma-international.org/ecma-262/5.1/#sec-11.9.3The comparison x == y, where x and y are values, produces true or false. Such a comparison is performed as follows: If Type(x) is the same as Type(y), then If Type(x) is Undefined, return true. If Type(x) is Null, return true. If Type(x) is Number, then If x is NaN, return false. If y is NaN, return false. If x is the same Number value as y, return true. If x is +0 and y is −0, return true. If x is −0 and y is +0, return true. Return false. If Type(x) is String, then return true if x and y are exactly the same sequence of characters (same length and same characters in corresponding positions). Otherwise, return false. If Type(x) is Boolean, return true if x and y are both true or both false. Otherwise, return false. Return true if x and y refer to the same object. Otherwise, return false. If x is null and y is undefined, return true. If x is undefined and y is null, return true. If Type(x) is Number and Type(y) is String, return the result of the comparison x == ToNumber(y). If Type(x) is String and Type(y) is Number, return the result of the comparison ToNumber(x) == y. If Type(x) is Boolean, return the result of the comparison ToNumber(x) == y. If Type(y) is Boolean, return the result of the comparison x == ToNumber(y). If Type(x) is either String or Number and Type(y) is Object, return the result of the comparison x == ToPrimitive(y). If Type(x) is Object and Type(y) is either String or Number, return the result of the comparison ToPrimitive(x) == y. Return false.
http://blog.csdn.net/wxdzxl/article/details/8502119
是先将a转换成bool类型 ,b转换成bool类型之后在进行比较吗?
但是我 用if(a==false)测试,结果还是相等.
== 不检查类型，只检查值。
在javascript里面： null, undefined, false, '' 的值都是false
if(a==false)测试,结果还是相等.
写错了
if(a==false) 测试结果是不相等的.
== 不检查类型，只检查值。
在javascript里面： null, undefined, false, '' 的值都是false
如果是 undefined的值是false的话
那么if(a==false)测试结果该是相等的,我测试的结果不是相等的.
但是 if(a==undefined) 结果却是相等的
== 不检查类型，只检查值。
在javascript里面： null, undefined, false, '' 的值都是false
如果是 undefined的值是false的话
那么if(a==false)测试结果该是相等的,我测试的结果不是相等的.
但是 if(a==undefined) 结果却是相等的
http://www.ecma-international.org/ecma-262/5.1/#sec-11.9.3The comparison x == y, where x and y are values, produces true or false. Such a comparison is performed as follows: If Type(x) is the same as Type(y), then
If Type(x) is Undefined, return true.
If Type(x) is Null, return true.
If Type(x) is Number, then
If x is NaN, return false.
If y is NaN, return false.
If x is the same Number value as y, return true.
If x is +0 and y is −0, return true.
If x is −0 and y is +0, return true.
Return false.
If Type(x) is String, then return true if x and y are exactly the same sequence of characters (same length and same characters in corresponding positions). Otherwise, return false.
If Type(x) is Boolean, return true if x and y are both true or both false. Otherwise, return false.
Return true if x and y refer to the same object. Otherwise, return false.
If x is null and y is undefined, return true.
If x is undefined and y is null, return true.
If Type(x) is Number and Type(y) is String,
return the result of the comparison x == ToNumber(y).
If Type(x) is String and Type(y) is Number,
return the result of the comparison ToNumber(x) == y.
If Type(x) is Boolean, return the result of the comparison ToNumber(x) == y.
If Type(y) is Boolean, return the result of the comparison x == ToNumber(y).
If Type(x) is either String or Number and Type(y) is Object,
return the result of the comparison x == ToPrimitive(y).
If Type(x) is Object and Type(y) is either String or Number,
return the result of the comparison ToPrimitive(x) == y.
Return false.
== 不检查类型，只检查值。
在javascript里面： null, undefined, false, '' 的值都是false
如果是 undefined的值是false的话
那么if(a==false)测试结果该是相等的,我测试的结果不是相等的.
但是 if(a==undefined) 结果却是相等的直接用if(a) 就可以了