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javascript_library.html
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javascript_library.html
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Javascript Library</title>
</head>
<body>
<script type="text/javascript">
var _ = {
map: function(arr, callback) {
var result = [];
for( var i = 0; i < arr.length; i++){
result.push(callback(arr[i]));
}
return result;
},
reduce: function(arr, callback, startval) {
if (!startval) {
var memo = arr[0];
var startidx = 1;
}else{
var memo = startval;
var startidx = 0;
}
for( var i = startidx; i < arr.length; i++){
memo = callback(memo, arr[i]);
}
return memo;
},
find: function(arr, callback) {
for (var i = 0; i < arr.length; i++){
if (callback(arr[i])){
return arr[i];
}
}
},
filter: function(arr, callback) {
var result = [];
for( var i = 0; i < arr.length; i++){
if( callback(arr[i])){
result.push(arr[i]);
}
}
return result;
},
reject: function(arr, callback) {
var wrong = [];
for( var i = 0; i < arr.length; i++){
if( !callback(arr[i])){
wrong.push(arr[i]);
}
}
return wrong;
}
}
// you just created a library with 5 methods!
var evens = _.filter([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
console.log(evens); // if things are working right, this will return [2,4,6].
var maps = _.map([1, 2, 3], function(num){ return num * 3; });
console.log(maps);
var sum = _.reduce([1, 4, 3], function(memo, num){ return memo * num; });
console.log(sum);
var correct = _.find([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
console.log(correct);
var wrong = _.reject([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
console.log(wrong);
</script>
</body>
</html>