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JavaScript

function alphabetPosition( text ) {
	var positions = [];
	for ( var i = 0; i < text.length; i++ ) {
  	var charCode = text.charCodeAt( i );
    if ( charCode >= 97 && charCode <= 122 ) {
    	positions.push( charCode - 96 );
    } else if ( charCode >= 65 && charCode <= 90 ) {
    	positions.push( charCode - 64 );
    }
  }
  return positions;
}

var positions = alphabetPosition( 'Hello World' );
console.log(positions);