Most of the loops you’ll write in CoffeeScript will be comprehensions over arrays, objects, and ranges. Comprehensions replace (and compile into) for loops, with optional guard clauses and the value of the current array index. Unlike for loops, array comprehensions are expressions, and can be returned and assigned.
# Eat lunch.
eat = (food) -> "#{food} eaten."
eat food for food in ['toast', 'cheese', 'wine']
​
# Fine five course dining.
courses = ['greens', 'caviar', 'truffles', 'roast', 'cake']
menu = (i, dish) -> "Menu Item #{i}: #{dish}"
menu i + 1, dish for dish, i in courses
​
# Health conscious meal.
foods = ['broccoli', 'spinach', 'chocolate']
eat food for food in foods when food isnt 'chocolate'
// Eat lunch.
var courses, dish, eat, food, foods, i, j, k, l, len, len1, len2, menu, ref;
​
eat = function(food) {
return `${food} eaten.`;
};
​
ref = ['toast', 'cheese', 'wine'];
for (j = 0, len = ref.length; j < len; j++) {
food = ref[j];
eat(food);
}
​
// Fine five course dining.
courses = ['greens', 'caviar', 'truffles', 'roast', 'cake'];
​
menu = function(i, dish) {
return `Menu Item ${i}: ${dish}`;
};
​
for (i = k = 0, len1 = courses.length; k < len1; i = ++k) {
dish = courses[i];
menu(i + 1, dish);
}
​
// Health conscious meal.
foods = ['broccoli', 'spinach', 'chocolate'];
​
for (l = 0, len2 = foods.length; l < len2; l++) {
food = foods[l];
if (food !== 'chocolate') {
eat(food);
}
}​
Comprehensions should be able to handle most places where you otherwise would use a
loop,
each/forEach,
map, or
select/filter, for example :
shortNames = (name for name in list when name.length < 5)
If you know the start and end of your loop, or would like to step through in fixed-size increments, you can use a range to specify the start and end of your comprehension.
