check if key exists in map javascript code example

Example 1: javascript does key exist

var person={"name":"Billy","age":20}
person.hasOwnProperty("name"); // true
person.hasOwnProperty("sex"); // false

Example 2: how to check if a key exists in an object javascript

!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj   // ERROR!  Equivalent to "false in obj"

Example 3: check if a key is in a map

if ( m.find("f") == m.end() ) {
  // not found
} else {
  // found
}

Example 4: js check if map contains key

const map1 = new Map();
map1.set('bar', 'foo');

console.log(map1.has('bar'));
// expected output: true

console.log(map1.has('baz'));
// expected output: false