everyBy

Test whether all elements in a collection pass a test implemented by a predicate function.

Usage

var everyBy = require( '@stdlib/utils/every-by' );

everyBy( collection, predicate[, thisArg ] )

Tests whether all elements in a collection pass a test implemented by a predicate function.

function isPositive( value ) {
    return ( value > 0 );
}

var arr = [ 1, 2, 3, 4 ];

var bool = everyBy( arr, isPositive );
// returns true

If a predicate function returns a non-truthy value, the function immediately returns false.

function isPositive( value ) {
    return ( value > 0 );
}

var arr = [ 1, -2, 3, 4 ];

var bool = everyBy( arr, isPositive );
// returns false

The invoked function is provided three arguments:

  • value: collection element
  • index: collection index
  • collection: input collection

To set the function execution context, provide a thisArg.

function sum( value ) {
    if ( value < 0 ) {
        return false;
    }
    this.sum += value;
    this.count += 1;
    return true;
}

var arr = [ 1, 2, 3, 4 ];

var context = {
    'sum': 0,
    'count': 0
};

var bool = everyBy( arr, sum, context );
// returns true

var mean = context.sum / context.count;
// returns 2.5

Notes

  • A collection may be either an Array, Typed Array, or an array-like Object (excluding strings and functions).

  • If provided an empty collection, the function returns true.

    function untrue() {
        return false;
    }
    var bool = everyBy( [], untrue );
    // returns true
    
  • The function differs from Array.prototype.every in the following ways:

    • The function does not skip undefined elements.

      function log( value, index ) {
          console.log( '%s: %s', index, value );
          return true;
      }
      
      var arr = [ 1, , , 4 ];
      
      var bool = everyBy( arr, log );
      /* =>
          0: 1
          1: undefined
          2: undefined
          3: 4
      */
      
    • The function provides limited support for dynamic collections (i.e., collections whose length changes during execution).

Examples

var randu = require( '@stdlib/random/base/randu' );
var everyBy = require( '@stdlib/utils/every-by' );

function isPositive( value ) {
    return ( value > 0 );
}

var bool;
var arr;
var i;

arr = new Array( 100 );
for ( i = 0; i < arr.length; i++ ) {
    arr[ i ] = randu();
}

bool = everyBy( arr, isPositive );
// returns <boolean>