there are many methods.
in
operator
The
in
operator returnstrue
if the specified property is in the specified object or its prototype chain.
how to use?
for example:
const dict = { a: "a", b: "b" }
console.log("a" in dict)
attention: the attribute name should be string.
that is to say:
- a in dict ❎
- "a" in dict ✅
Object API: hasOwnProperty
Object.prototype.hasOwnProperty() - JavaScript | MDN
The complete expression is Object.prototype.hasOwnProperty()
.
how to use it ?
const dict = {
a: "a",
b: "b",
}
console.log(dict.hasOwnProperty("a"))
the same is the attribute key should be a string.
- a in dict ❎
- "a" in dict ✅
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