How to use if including comma expressions in JavaScript

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Sometimes you will see that the if judgment in JavaScript contains a comma "," which is actually a comma expression. In the if condition, only the last expression plays a role in judgment.

Take a look at the following example:

Let a = 1, b = 2, c = 3 if only judges the last expression if (a = 10, b = 20, c = 3) {console.log ("c = = 3");} else {console.log ("c! = 3")} / / console output: / / c = = 3

There are three expressions in if above, the first two are not valid, only the last one is true, and only the last one is judged in if, so the result is true.

Although if only determines that there is the most one expression, the previous expression is also executed.

Please refer to the following code:

Let a = 10, b = 20, c = 30 if only judges the last expression, but the previous expression also executes if (a = 1, b = 2, c = 3) {console.log ("c = = 3");} else {console.log ("c! = 3")} / / console output: / / c! = 3console.log (a, b) / / console output: / / 1 2

In the if judgment, the last condition c = = 3 is not true, so the if judgment is false.

But the first two expressions were executed, so in the end, axiom 1 was bounded 2.

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