[英]In Javascript, how to apply a dynamically created function name
My goal is to efficiently apply a dynamically chosen set of transforms to each element of a matrix. 我的目标是有效地将动态选择的变换集应用于矩阵的每个元素。 I store the selected functions in an array, then apply each of them in a single pass thru the matrix. 我将选定的函数存储在一个数组中,然后通过矩阵一次性地应用它们。
My question is, how can I dynamically create the name of a function that I add to the array of functions? 我的问题是,如何动态创建我添加到函数数组的函数的名称?
This fiddle contains my attempt. 这个小提琴包含了我的尝试。 My question is included in the comment block. 我的问题包含在评论栏中。
function dynam () {
var prepend = 'before - ';
var append = ' - after';
var whichCase = 'Upper';
var functionsToApply = [];
var matrix = [
['aBc', 'DeF'],
['ghi', 'JKL'],
];
var out = 'Initial: ' + matrix.join(' | ');
document.getElementById('output').innerHTML = out + '\n';
console.log(out);
// Set up transforms
if (whichCase == 'Lower') {
functionsToApply.push(function(v) {return v.toLowerCase();});
} else if (whichCase == 'Upper'){
functionsToApply.push(function(v) {return v.toUpperCase();});
}
// How can the function be defined dynamically?
// Perhaps something like:
// if(['Lower','Upper'].indexOf(whichCase) != -1) {
// functionsToApply.push(function(v) {'return v.to' + which + 'Case();'});
// }
if (prepend && prepend.length > 0 && prepend != 'none') {
functionsToApply.push(function(v) {return prepend + v;});
}
if (append && append.length > 0 && append != 'none') {
functionsToApply.push(function(v) {return v + append;});
}
// Apply all of the transforms to each of the elements of the matrix
matrix = matrix.map(function(row){
return row.map(function(val) {
for (var fn = 0; fn < functionsToApply.length; fn++) {
val = functionsToApply[fn](val);
}
return val;
})
});
out = 'Final: ' + matrix.join(' | ');
document.getElementById('output').innerHTML += out + '\n';
console.log(out);
}
I like to declare my functions in a hash in this case, then you can call them based on the value passed in, which is the key to the hash. 在这种情况下,我喜欢在哈希中声明我的函数,然后你可以根据传入的值来调用它们,这是哈希的关键。
Updated: I've added a way to get the lower/upper function dynamically, and call it. 更新:我添加了一种动态获取下/上功能的方法,并调用它。
function dynam(whichCase, prepend, append, matrix) { var functionHash = { "Lower" : function(v) {return v.toLowerCase();}, "Upper" : function(v) {return v.toUpperCase();}, "Prepend" : function(v) {return prepend + v;}, "Append": function(v) {return v + append;} } // to actually get the case function based on the word passed in, // you can do it this way. var lowerUpperFunction = String.prototype['to' + whichCase + 'Case']; var str = lowerUpperFunction.call("xyz"); console.log(str); var functionsToApply = []; var out = 'Initial: ' + matrix.join(' | '); console.log(out); // see how we just take the whichCase and make that a call to the hash? functionsToApply.push(functionHash[whichCase]); if (prepend && prepend.length > 0 && prepend != 'none') { functionsToApply.push(functionHash["Prepend"]); } if (append && append.length > 0 && append != 'none') { functionsToApply.push(functionHash["Append"]); } // Apply all of the transforms to each of the elements of the matrix matrix = matrix.map(function(row){ return row.map(function(val) { for (var fn = 0; fn < functionsToApply.length; fn++) { console.log("applying function to val" + val ); val = functionsToApply[fn](val); } return val; }) }); out = 'Final: ' + matrix.join(' | '); return out; } var p = 'before - '; var a = ' - after'; var w = 'Upper'; var m = [ ['aBc', 'DeF'], ['ghi', 'JKL'], ]; console.log( dynam(w, p, a, m) );
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