在JS中，“==”符号不检查变量的类型。因此，“0”= 0 = false(在JS中为0 = false)，在这种情况下将返回true，但如果使用“===”，结果将为false。

当你使用"if"时，在以下情况下它将是"false":

[0, false, '', null, undefined, NaN] // null = undefined, 0 = false

So

if("0") = if( ("0" !== 0) && ("0" !== false) && ("0" !== "") && ("0" !== null) && ("0" !== undefined) && ("0" !== NaN) )
        = if(true && true && true && true && true && true)
        = if(true)

0周围的引号使它成为一个字符串，它的值为true。

删除引号，它应该工作。

if (0) console.log("ha") 

这都是因为ECMA规格…"0" == false，因为这里指定的规则http://ecma262-5.com/ELS5_HTML.htm#Section_11.9.3…if('0')的结果为true，因为这里指定的规则http://ecma262-5.com/ELS5_HTML.htm#Section_12.5

在PHP中，字符串“0”是假的(false-when-used-in-boolean-context)。在JavaScript中，所有非空字符串都是真值。

技巧是==针对布尔值并不在布尔上下文中求值，它转换为数字，在字符串的情况下是通过解析为十进制来完成的。所以你得到0而不是truthiness boolean true。

这是一个非常糟糕的语言设计，这也是我们尽量不使用不幸的==操作符的原因之一。请使用===代替。

这是按规格的。

12.5 The if Statement 
.....

2. If ToBoolean(GetValue(exprRef)) is true, then 
a. Return the result of evaluating the first Statement. 
3. Else, 
....

根据规范，ToBoolean是

抽象操作ToBoolean根据表11将其参数转换为Boolean类型的值:

这个表格是这样描述字符串的:

如果参数为空String(其长度为零)，则结果为假; 否则结果为真

现在，为了解释为什么"0" == false，您应该读取相等运算符，它表示它从抽象操作GetValue(lref)中获得其值，与右侧的相同。

将相关部分描述为:

if IsPropertyReference(V), then 
a. If HasPrimitiveBase(V) is false, then let get be the [[Get]] internal method of base, otherwise let get
be the special [[Get]] internal method defined below. 
b. Return the result of calling the get internal method using base as its this value, and passing 
GetReferencedName(V) for the argument

或者换句话说，字符串有一个基元，它会回调内部的get方法，结果看起来是false。

如果你想用GetValue运算来求值，请使用==，如果你想用ToBoolean运算，请使用===(也称为“严格”相等运算符)

The "if" expression tests for truthiness, while the double-equal tests for type-independent equivalency. A string is always truthy, as others here have pointed out. If the double-equal were testing both of its operands for truthiness and then comparing the results, then you'd get the outcome you were intuitively assuming, i.e. ("0" == true) === true. As Doug Crockford says in his excellent JavaScript: the Good Parts, "the rules by which [== coerces the types of its operands] are complicated and unmemorable.... The lack of transitivity is alarming." It suffices to say that one of the operands is type-coerced to match the other, and that "0" ends up being interpreted as a numeric zero, which is in turn equivalent to false when coerced to boolean (or false is equivalent to zero when coerced to a number).