An equal sign is an assignment, and the main problem is the difference between two equals and three equals. The difference between two equals and three equals in javaScript

In short: == convert the type first and then compare, === determine the type first, if not the same type is false. === = is equal to, the two sides of the comparison have to be absolutely the same

Alert (0 = = ""); / / true Alert (0 = = false); / / true Alert (” = = false ”); / / true

Alert (0 = = = ""); / / false Alert (0 = = = false); / / false Alert (” = = = false ”); / / false

First say ===, this is relatively simple, specific comparison rules are as follows: 1. If the type is different, it is [unequal] 2. If both are numerical values and the same value, then [equal]; (! The exception is, if at least one of them is NaN, then [not equal]. (to determine whether a value isNaN, you can only use isNaN().) 3. If both are strings and the characters in each position are the same, then [equal]; Otherwise [unequal]. 4. If both values are true or both values are false, then [equal]. 5. If both values refer to the same object or function, then [equal]; Otherwise [unequal]. 6. If both values are null or both are undefined, then [equal].

Again ==, the specific comparison rules are as follows:

1. If the two values are of the same type, make a === comparison. The comparison rule is the same as above 2. If two values are of different types, they may be equal. Type conversion and comparison according to the following rules: A. If one is null and the other is undefined, then [equal]. B. If one is a string and the other is a number, convert the string to a number for comparison. C. If any value is true, convert it to 1 for comparison; If either value is false, convert it to 0 for comparison. D. If one is an object and the other is a value or string, convert the object to a value of the underlying type for comparison. Object to the underlying type, using its toString or valueOf methods. Js core built-in class, will try valueOf before toString; The exception is Date, which takes advantage of the toString transformation. Non-js core objects, let say (more trouble, I do not understand) E. Any other combination (array, array, etc.) is [unequal].

When a person can not find a way out of the time, the best way is to do the current can do the best, no one can do.