Day 5: The every helper
The every helper is used to find whether all the elements in a given list pass a specific condition.
The condition is passed in the iterator function, and it executes that function once for each element in the list.
If, for any element, the iterator function returns false, every() returns false. Otherwise, it returns true.
Syntax
array.every(function(currentValue, index, arr), thisValue)
- currentValue: Required. The value of the current element
- index: Optional The array index of the current element
- arr: Optional. The array object the current element belongs to
- thisValue: Optional. A value to be passed to the function to be used as its “this” value.
Simple Example
When the users submit a form, suppose that all the fields are taken out in an array before submitting the form. You have to validate that every field has atleast 1 character
const fieldData1 = [ 'Dan', 'abc@xyz.com', '21', 'Delhi', '' ];
const fieldData2 = [ 'John', 'efg@pqr.com', '25', 'Delhi', 'Student' ];
// Without `every`
function validateFields (fields) {
let allFieldsValid = true;
for (let i=0; i<fields.length; i++) {
if (fields[i].length === 0)
allFieldsValid = false;
}
return allFieldsValid;
}
console.log ("Validating Fields without every: ");
console.log ("fieldData1: ", validateFields(fieldData1));
console.log ("fieldData2: ", validateFields(fieldData2));
// With every, without arrow function
function validateFields2 (fields) {
return fields.every (function (field) {
return field.length > 0;
});
}
console.log ("Validating Fields with every: ");
console.log ("fieldData1: ", validateFields2(fieldData1));
console.log ("fieldData2: ", validateFields2(fieldData2));
// With every, with arrow function (one liner)
const validateFields3 = fields => fields.every (field => field.length>0);
console.log ("Validating Fields with every: ");
console.log ("fieldData1: ", validateFields3(fieldData1));
console.log ("fieldData2: ", validateFields3(fieldData2));
Another Simple example
Slots of people are sent for driving license test, check whether each person in a slot is 18 years or above
const slot1 = [
{ name: 'John', age: 16 },
{ name: 'Matt', age: 20 },
{ name: 'Dan', age: 17 },
];
const slot2 = [
{ name: 'Amanda', age: 32 },
{ name: 'Kepler', age: 20 },
{ name: 'Stan', age: 25 },
];
// Without arrow functions
function validateSlot (slot) {
return slot.every (function (person) {
return person.age >= 18;
});
}
console.log ("Result 1 \n------------------");
console.log ("Slot 1: ", validateSlot (slot1));
console.log ("Slot 2: ", validateSlot (slot2));
console.log ("------------------");
// With arrow functions
const validateSlot2 = slot => slot.every (person => person.age>=18);
console.log ("Result 2 \n------------------");
console.log ("Slot 1: ", validateSlot2 (slot1));
console.log ("Slot 2: ", validateSlot2 (slot2));
Homework for you
Check whether a set of numbers is
- Even
- Odd
- Prime
- Negative
- Positive
- Perfect Square
Feel free to add more :)
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