What does find return JavaScript?

The find() method returns the value of the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned.

find will search the array for the first element which, when used as an argument of the callback, will have the callback return a truthy value. If nothing is found, it returns undefined .

Technically speaking, find always returns a value, but that value could be a reference if the item you’re looking for is an object. It will still be a value nonetheless.

Return value: It returns the array element value if any of the elements in the array satisfy the condition, otherwise it returns undefined.

YES, use it always with for … in There are some nice answers here describing what hasOwnProperty() does and offering other solutions.

What is the difference between find() and filter() methods in JavaScript ? The find() method is used to find all the descendant elements of the selected element. … The filter() method is used to filters all the elements and returns the element that matches and the element that do not match are removed.

Find returns 0 if it exits successfully, even if it didn’t find a file (which is a correct result not indicating an error when the file indeed doesn’t exist).

1. const simpleArray = [3, 5, 7, 15];
2. const objectArray = [{ name: ‘John’ }, { name: ‘Emma’ }]
3. console. log( simpleArray. find(e => e === 7) )
4. console. log( simpleArray. find(e => e === 10) )
5. console. log( objectArray. find(e => e. name === ‘John’) )

The in operator returns true if the specified property is in the specified object or its prototype chain.

The indexOf() method returns the index within the calling String object of the first occurrence of the specified value, starting the search at fromIndex . Returns -1 if the value is not found.

In javascript strict mode, undefined is not false, but javascript try to convert the object or var to a boolean value (this is called in javascript truthy value), that’s the reason you got an undefined as false.

The filter() method creates a new array with all elements that pass the test implemented by the provided function.

If it is undefined, it will not be equal to a string that contains the characters “undefined”, as the string is not undefined. You can check the type of the variable: if (typeof(something) != “undefined”) …

The function ‘fetchrow_arrayref()‘ returns a reference to an array of row values. Explanation: ‘fetchrow_arrayref()’ returns a reference to an array of row values.

The filter() method creates a new array filled with elements that pass a test provided by a function. The filter() method does not execute the function for empty elements. The filter() method does not change the original array.

The hasOwnProperty() method in JavaScript is used to check whether the object has the specified property as its own property. This is useful for checking if the object has inherited the property rather than being it’s own.

The hasOwnProperty() method returns a boolean indicating whether the object has the specified property as its own property (as opposed to inheriting it).

hasOwnProperty allows us to test only for properties we have manually created on the current object. In most cases where we use the keyword in as in “property” in Object, we can replace it with hasOwnProperty to make sure we are testing for stuff we created ourselves.

Find and Filter The find() method returns the first value that matches from the collection. Once it matches the value in findings, it will not check the remaining values in the array collection. The filter() method returns the matched values in an array from the collection.

To our surprise, for-loops are much faster than the Array. filter method. To be precise, the Filter method is 77% slower than for loop.

Splice and Slice both are Javascript Array functions. Splice vs Slice. The splice() method returns the removed item(s) in an array and slice() method returns the selected element(s) in an array, as a new array object. The splice() method changes the original array and slice() method doesn’t change the original array.

Indeed, grep returns 0 if it matches, and non-zero if it does not.

When a bash function ends its return value is its status: zero for success, non-zero for failure. To return values, you can set a global variable with the result, or use command substitution, or you can pass in the name of a variable to use as the result variable.

1. Return true if a bash variable is unset or set to the empty string: if [ -z “$var” ];
2. Another option: [ -z “$var” ] && echo “Empty”
3. Determine if a bash variable is empty: [[ ! -z “$var” ]] && echo “Not empty” || echo “Empty”

Python String find() The find() method returns the index of first occurrence of the substring (if found). If not found, it returns -1.

Definition and Usage The find() method finds the first occurrence of the specified value. The find() method returns -1 if the value is not found. The find() method is almost the same as the index() method, the only difference is that the index() method raises an exception if the value is not found. (

The JavaScript array prototype constructor is used to allow to add new methods and properties to the Array() object. If the method is constructed, then it will available for every array. When constructing a property, All arrays will be given the property, and its value, as default. Syntax: Array.prototype.name = value.

In javascript the => is the symbol of an arrow function expression. A arrow function expression does not have its own this binding and therefore cannot be used as a constructor function.

(three dots in JavaScript) is called the Spread Syntax or Spread Operator. This allows an iterable such as an array expression or string to be expanded or an object expression to be expanded wherever placed.

The three dots in JavaScript are the spread / rest operator. The spread syntax allows an expression to be expanded in places where multiple arguments are expected. The rest parameter syntax is used for functions with a variable number of arguments. The spread / rest operator for arrays was introduced in ES6.

The indexOf() method returns the first index at which a given element can be found in the array, or -1 if it is not present. Because arrays are 0 based, returning 0 would mean starting from the first character was matched; 1, the second character, and so on.

indexOf() method returns the index of the first matching item in an array (or -1 if it doesn’t exist). var wizards = [‘Gandalf’, ‘Radagast’, ‘Saruman’, ‘Alatar’]; // Returns 1 wizards. … But… that doesn’t work if the array contains objects instead of simple strings or numbers.

The indexOf() method returns the position of the first occurrence of specified character(s) in a string. Tip: Use the lastIndexOf method to return the position of the last occurrence of specified character(s) in a string.

Checking for falsy values on variables It is possible to check for a falsy value in a variable with a simple conditional: if (! variable) { // When the variable has a falsy value the condition is true. }

undefined is true because undefined implicitly converts to false , and then ! negates it. Collectively, those values (and false ) are called falsy values. (Anything else¹ is called a truthy value.)

ValueDescriptionfalseThe keyword false .0The Number zero (so, also 0.0 , etc., and 0x0 ).-0The Number negative zero (so, also -0.0 , etc., and -0x0 ).

The filter() method returns an array containing elements of the parent array that match the set test. A function containing a test is passed as an argument to the filter method. To keep an element the test function should return true and false to discard an element.

reduce() method in JavaScript is used to reduce the array to a single value and executes a provided function for each value of the array (from left-to-right) and the return value of the function is stored in an accumulator. Syntax: array.reduce( function(total, currentValue, currentIndex, arr), initialValue )

The filter() method creates a new array with all the elements that pass the test implemented by the callback() function. Internally, the filter() method iterates over each element of the array and pass each element to the callback function.

A function returns undefined if a value was not returned. , One reason to use typeof is that it does not throw an error if the variable has not been declared. , You can use undefined and the strict equality and inequality operators to determine whether a variable has a value.