与逻辑的执行问题，更多是配合或来使用，但是工作中遇到了下面代码，没见过，学习一下。
条件语句的使用,下文意思为a存在成立，b也存在，c也满足，再执行h=0语句。
a&& b&& c &&
(h = 0);
其余可以参考：
blog.csdn.net/qq_21972797…
备注：
The logical AND (&&) operator (logical conjunction) for a set of operands is true if and only if all of its operands are true. It is typically used with Boolean (logical) values. When it is, it returns a Boolean value. However, the && operator actually returns the value of one of the specified operands, so if this operator is used with non-Boolean values, it will return a non-Boolean value.
If expr1 can be converted to true, returns expr2; else, returns expr1.
If a value can be converted to true, the value is so-called truthy. If a value can be converted to false, the value is so-called falsy.
Examples of expressions that can be converted to false are:
null;NaN;0;- empty string (
""or''or``); undefined.
Even though the && operator can be used with operands that are not Boolean values, it can still be considered a boolean operator since its return value can always be converted to a boolean primitive. To explicitly convert its return value (or any expression in general) to the corresponding boolean value, use a double NOT operator or the Boolean (en-US) constructor.
Short-circuit evaluation
The logical AND expression is evaluated left to right, it is tested for possible "short-circuit" evaluation using the following rule:
(some falsy expression) && expr is short-circuit evaluated to the falsy expression;
Short circuit means that the expr part above is not evaluated, hence any side effects of doing so do not take effect (e.g., if expr is a function call, the calling never takes place). This happens because the value of the operator is already determined after the evaluation of the first operand. See example:
function A(){ console.log('called A'); return false; }
function B(){ console.log('called B'); return true; }
console.log( A() && B() );
// logs "called A" due to the function call,
// then logs false (which is the resulting value of the operator)
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Operator precedence
The following expressions might seem equivalent, but they are not, because the && operator is executed before the || operator (see operator precedence).
true || false && false // returns true, because && is executed first
(true || false) && false // returns false, because operator precedence cannot apply
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Examples
Using AND
The following code shows examples of the && (logical AND) operator.
a1 = true && true // t && t returns true
a2 = true && false // t && f returns false
a3 = false && true // f && t returns false
a4 = false && (3 == 4) // f && f returns false
a5 = 'Cat' && 'Dog' // t && t returns "Dog"
a6 = false && 'Cat' // f && t returns false
a7 = 'Cat' && false // t && f returns false
a8 = '' && false // f && f returns ""
a9 = false && '' // f && f returns false
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Conversion rules for booleans
Converting AND to OR
The following operation involving booleans:
bCondition1 && bCondition2
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is always equal to:
!(!bCondition1 || !bCondition2)
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Converting OR to AND
The following operation involving booleans:
bCondition1 || bCondition2
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is always equal to:
!(!bCondition1 && !bCondition2)
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Removing nested parentheses
As logical expressions are evaluated left to right, it is always possible to remove parentheses from a complex expression following some rules.
The following composite operation involving booleans:
bCondition1 || (bCondition2 && bCondition3)
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is always equal to:
bCondition1 || bCondition2 && bCondition3
