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百度 从历史上看，秦汉的政治文化、行政习惯构成了古代中国帝制的基本框架，由此形成的国家礼乐建制、文化活动、艺术形态等促成了中国文学格局中最为基础的“制度文学”，即作为国家政治行为和行政运作的文学活动及其表达方式。

A falsy (sometimes written falsey) value is a value that is considered false when encountered in a Boolean context.

JavaScript uses type conversion to coerce any value to a Boolean in contexts that require it, such as conditionals and loops.

The following table provides a complete list of JavaScript falsy values:

Value Type Description
null Null The keyword null — the absence of any value.
undefined Undefined undefined — the primitive value.
false Boolean The keyword false.
NaN Number NaN — not a number.
0 Number The Number zero, also including 0.0, 0x0, etc.
-0 Number The Number negative zero, also including -0.0, -0x0, etc.
0n BigInt The BigInt zero, also including 0x0n, etc. Note that there is no BigInt negative zero — the negation of 0n is 0n.
"" String Empty string value, also including '' and ``.
document.all Object The only falsy object in JavaScript is the built-in document.all.

The values null and undefined are also nullish.

Examples

Examples of falsy values in JavaScript (which are coerced to false in Boolean contexts, and thus bypass the if block):

js
if (false) {
  // Not reachable
}

if (null) {
  // Not reachable
}

if (undefined) {
  // Not reachable
}

if (0) {
  // Not reachable
}

if (-0) {
  // Not reachable
}

if (0n) {
  // Not reachable
}

if (NaN) {
  // Not reachable
}

if ("") {
  // Not reachable
}

The logical AND operator, &&

If the first object is falsy, it returns that object:

js
console.log(false && "dog");
// ? false

console.log(0 && "dog");
// ? 0

See also