There are three logical operators in js: logical NOT!, logical AND &&, and logical OR ||. The so-called short-circuit operation is that when the value of the first operand of && is false, the value of the first operand is returned directly without calculating the second operand;
var bar1 = 0&&c; console.log('bar1====='+bar1); //bar1=====0 var foo1 = 5&&c; console.log('foo1===='+foo1); //报c is not defined错误。
When || When the value of the first operand is true, the value of the first operand is returned directly without calculating the second operand;
var foo = 5||c;console.log('foo===='+foo);//foo====5 不报错var bar = 0||c;console.log('bar===='+bar);//报c is not defined错误。
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